What attack rolls does a TWF 3 Rogue/1 White-haired Witch get?

Question

The White-Haired Witch gains a powerful natural attack (that automatically grapples when it hits). How many attacks do a 3 Knife Master/1 Winter Witch I get for a full round attack, and what are those attack rolls?

Assume Str 10, Dex 20, Int 16, TWF, BAB+2.

-2/-2 [TWF feat, wielding 2 light weapons], +5 [Dex 20 and Weapon Finesse], +2 [BAB of 2]= +5 and +5 for the knife attacks, right? Since the natural attack is a different limb it gets added as secondary attack for -5, +5 [Dex+finesse should apply because natural weapons are light; however the spell replaces the strength modifier with intelligence, so not sure if that's correct? However the Hex describes it as a limb with full dexterity.]

Additional information:

White Hair (Su): At 1st level, a white-haired witch gains the ability to use her hair as a weapon. This functions as a primary natural attack with a reach of 5 feet. The hair deals 1d4 points of damage (1d3 for a Small witch) plus the witch’s Intelligence modifier. In addition, whenever the hair strikes a foe, the witch can attempt to grapple that foe with her hair as a free action* without provoking an attack of opportunity, using her Intelligence modifier in place of her Strength modifier when making the combat maneuver check. When a white-haired witch grapples a foe in this way, she does not gain the grappled condition.

This seems like a permanent version of this hex (which it replaces, along with all other hexes).

Prehensile Hair (Su): The witch can instantly cause her hair (or even her eyebrows) to grow up to 10 feet long or to shrink to its normal length, and can manipulate her hair as if it were a limb with a Strength score equal to her Intelligence score. Her hair has reach 10 feet, and she can use it as a secondary natural attack that deals 1d3 points of damage (1d2 for a Small witch). Her hair can manipulate objects (but not weapons) as dexterously as a human hand. The hair cannot be sundered or attacked as a separate creature. Pieces cut from the witch’s elongated hair shrink away to nothing. Using her hair does not harm the witch’s head or neck, even if she lifts something heavy with it. The witch can manipulate her hair a number of minutes each day equal to her level; these minutes do not need to be consecutive, but must be spent in 1-minute increments. A typical male witch with this hex can also manipulate his beard, moustache, or eyebrows.

Answer 1

First, it doesn't matter what the ability looks like

3.X (including here 3.0, 3.5, Pathfinder, and the semi-combined "system" referred to as 3.PF) is a rules-heavy, legalistic system. The idea that the hair-based natural attack "looks like" a hex or indeed any other ability isn't relevant unless it specifically references those abilities for some reason. Since it doesn't reference the Prehensile Hair hex, the wording of that hex is not relevant to the natural attack.

Aside from that, you're correct

From the PFSRD:

You can make attacks with natural weapons in combination with attacks made with a melee weapon and unarmed strikes, so long as a different limb is used for each attack. For example, you cannot make a claw attack and also use that hand to make attacks with a longsword. When you make additional attacks in this way, all of your natural attacks are treated as secondary natural attacks, using your base attack bonus minus 5 and adding only 1/2 of your Strength modifier on damage rolls. Feats such as Two-Weapon Fighting and Multiattack can reduce these penalties.

But it's interesting to note that you don't count as grappled if your hair manages to snag an enemy - that means, among other things, that you can attack your foe freely (they're denied their dexterity bonus, so free Sneak Attacks all day long) and that technically, by RAW you don't have to stay close to them to maintain the grapple because, well, you're "not grappling" them. Good luck getting that to fly past your DM, but it's an interesting bit of RAW.