Note: What the question posits doesn't do what the querent wants it to, but I've gone through the steps anyway so it can be seen where the process falls apart. Skip to the end if uninterested in the process's nuts and bolts.
First, apply inherited templates in a legal order...
Officially, the Dungeons and Dragons 3.5 rules from the Monster Manual for applying templates supersede the Dungeons and Dragons, Third Edition rules from Savage Species, including that text's type pyramid (142-4). An individual DM can, of course, adapt those rules to Dungeons and Dragon 3.5, but needn't (and, I'd advise, shouldn't). The Monster Manual on Acquired and Inherited Templates says that
Other templates, known as inherited templates, are part of a creature from the beginning of its existence. Examples include the celestial, fiendish, half-celestial, half-dragon, and half-fiend templates—all assume the creature was born with the template. (291)
and on Reading a Template says that
If a template changes the base creature’s type, the creature also acquires the augmented subtype (see page 306) unless the template description indicates otherwise. The augmented subtype is always paired with the creature’s original type. For example, a unicorn with the half-celestial template is an outsider with the augmented magical beast subtype. Unless a template indicates otherwise, the new creature has the traits of the new type but the features of the original type. (291)
So templates, then, alter the creature in the ways they say they alter the creature. Order can be important, but templates do what templates do.
Anyway, the template half-fey (Fiend Folio 89-90) says that the template
is an inherited template that can be added to any corporeal living creature... . The creature’s type changes to fey.
The template unseelie fey (Dragon Compendium Volume 1 222-3) says that the template
can be added to any living creature type... The creature's type becomes "fey." (223)
The omission of either acquired or inherited is odd as templates are either one or the other (MM 291), so just looking at the template unseelie fey puts the reader in house rules territory. Confer with the DM, but the description indicates the template should probably be an inherited one:
The offspring of [evil fey] liaisons [with other creatures] are unusual creatures, blending characteristics of both parents, sometimes able to pass as a parent's creature type. In turn, these half-breeds mate and pass on a blend of features and abilities. After several generations, these mixed creatures often resemble things out of nightmares or a mad wizard's experiment. (222)
Either way, at least one and I assume both templates must be applied to the creature first, so I'm going to apply these templates to a moon elf, making the moon elf's type fey (augmented fey, augmented humanoid).1,2,3
...Then apply acquired templates in whatever order the DM allows...
Before trying to do more, finish the remaining steps of character creation (PH 6).
Becoming a Divine Minion
The creature gains its level 1 feat during character creation, and it needs to pick this feat:
- The regional feat Otherworldly (Player's Guide to Faerûn 41-2) turns into a native outsider a deep imaskari (Underdark 9-10), spirit folk (Unapproachable East 13-14), or elf.4 As a Forgotten Realms regional feat, this must be taken at level 1, and it must be the creature's only regional feat.
This (or something like this) must be done because, otherwise, the template divine minion can't be acquired. The Magic Books of Faerûn Web column "Hate of the Cobra (Spells from the Church of Set)" says
that [the template Mulhorandi divine minion] can be added to any humanoid, monstrous humanoid, humanoid or monstrous humanoid with the celestial or fiendish template, or humanoid-shaped outsider...
And, unfortunately, fey isn't one of the listed types. So the half-fey unseelie fey moon elf from Evermeet cleric 1 of Set after having taken the feat Otherworldly—her type changing to outsider (native, augmented humanoid, augmented fey ×2)—, is then picked by a Mulhorandi god to become a divine minion. That's despite
The vast majority [of divine minions] resembl[ing] Mulhorandi men or women... . Most divine minions are created from a god's mortal servants (usually humans with six or more class levels in barbarian, fighter, paladin, or rogue)
but whatever. It happened.5,6
Becoming a Ghost
Then the divine minion half-fey unseelie fey moon elf from Evermeet cleric 1 of Set with the feat Otherworldly has adventures until she achieves enough XP to advance to level 2.
The Savage Progressions Web column "Gaining a Template Midcampaign" on the General Rules for Template Classes says that
A character may take a level in a template class as long as the DM approves and the character has earned enough XP to gain a level.
Now, I don't really know what happens at this point narratively to reflect the game's mechanics because, here, the character's supposed to die then advance as a ghost. That's not usually a choice. A character doesn't just, like, go around stabbing himself and hoping. But let's say the DM approves.
What this also means is that a creature can't enter play with only a template class.7 Silver lining? The template class ghost isn't restricted to specific types like the for-reals template ghost (MM 116-8), instead
"Ghost" is an acquired template usually gained upon an intelligent creature's death.
Thus, the divine minion half-fey unseelie fey moon elf from Evermeet cleric 1 of Set / ghost 1, upon having gained that first level in the template class ghost, gains the natural ability undeath, and
her type changes to "undead (augmented humanoid)," and she gains all the normal benefits and drawbacks that go with that type.
And, while I know it's silly for, for example, a beholder, displacer beast, or even a divine minion half-fey unseelie fey moon elf from Evermeet cleric 1 of Set to have its type and subtypes changed by the template class ghost first level ability undeath to undead (augmented humanoid), that is what happens, the quotation marks making sure you write that down on your character sheet exactly like it says.
Whatever types and subtypes the creature had struggled to acquire before now are obviated by—I kid you not—those quotation marks in the template class ghost's ability undeath, that specific ability overriding the general rules on Reading a Template (MM 291).
(Note that a generous DM may allow this level 2 creature to use from the Player's Handbook II the rules for Class Level Rebuilding (197-8) to replace that level of cleric with a level of the template class ghost.)
...But this combination of templates doesn't allow the creature enter the prestige class fiend of possession
The prestige class fiend of possession (Fiend Folio 204-7) has as a requirement that the character's race be outsider with the evil subtype. When all's said and done, the divine minion half-fey unseelie fey moon elf from Evermeet or Sidëyuir cleric 1 / ghost 1 is an undead (augmented humanoid).
- The minor ritual Ritual of Alignment (SS 148) takes a level 7 caster with the evil domain 1 day to perform. You'll pay 56,000 gp, 2,240 XP, and make a Will save (DC 10 if you're already evil). Success means gaining the subtype evil.
- The major ritual Wish (SS 150) takes a level 17 caster (who can cast spell wish, obviously) 1 standard action to perform. You'll pay at least 26,530 gp, and the DM's allowed to be a jerk and deny you all the cool stuff of the new form, but, if nothing else, you'll probably get the creature's type and maybe its subtypes. Hell, shoot for a balor, I guess?
- Under laboratory conditions and using a strict reading of prestige class requirements, the 4th-level Clr spell lesser infernal transformation [trans] (Spell Compendium 122) for 1 round/level changes the caster's type to outsider (baatezu, evil, lawful). The creature then must gain enough XP to advance a level while affected by the spell. Once that's done, the spell can be allowed to lapse but the creature can continue taking levels in the prestige class. (Tip: This is considered by some to be at least mildly shady.)
1 Keep in mind that some contend the template unseelie fey should have a higher Level Adjustment than +0 (q.v. threads from 2011 and 2013).
2 The creature's challenge rating, however, should be increased by +1 as per the Compendium errata.
3 The DM can look at such a character with a jaundiced eye, however, and totally choose not to allow the half-fey unseelie fey into the campaign. Really, such a DM may opine, can a creature's type change to the creature type it already is? Or, alternatively, can a creature's type become the creature type the creature already has?
4 I guessed that you'd pick elf, but, given the question, who knows?
5 Scholars suspect alcohol was a factor.
6 I'm guessing that the template divine minion was included because of this:
The creature's type changes to outsider, and any alignment subtypes it has changes to match the corresponding alignment subtypes of its deity.
Yet a typical creature has no alignment subtypes to change, and neither does, for example, a half-fey unseelie fey moon elf from Evermeet cleric 1 of Set with the feat Otherworldly. A DM who owes you money might, in exchange for blanking the debt, grant a divine minion a subtype anyway, but as written, the template doesn't grant one.
7 At level 1 a character is created (PH 6); after level 1, levels are advanced (PH 58-9).