Can you even mix races in D&D 3.5e? Is it allowed to have a multi-race character?
You can't apply multiple races to one character, except under unusual circumstances where some special feature explicitly says you can.
There are specific races called half-orcs and half-elves, for example (the unsaid other half is human), but you can't just be a "1/4 gnome 1/2 elf 1/4 human."
Of course there are some specialized templates, like half-dragon, all of which have rules of their own you'd need to read and understand and have GM approval to use. Same with using any monster race as a character, those have level adjustments and such - see the SRD section on Monsters as Races.
OK, having said that, from your other question it doesn't appear that you and your players are playing D&D 3.5e using the printed rules pretty much at all. You can't multi-race, you can't be multi-class at level 1 (you take a single class with a single level, unless you're using the Gestalt rules), and so on. Effectively you're playing Calvinball, not D&D.
And that's totally fine. You don't have to use the rules. Sure, let someone be 1/9 a bunch of races, you do you. But if you aren't using the real D&D, then we can't really help you with questions on this site because the only answer is "make it up yourself." We can deal with questions here that:
- Use the real rules - which require you to read those rules
- Use new house rules you've come up with that you can coherently explain to us
But that's about it. If you are trying to learn the real rules, feel free and ask us about them (but please show research effort by reading them first - you don't seem to have read any of the basic character creation rules given these questions). If you are trying to come up with house rules, we can give you balance feedback but you have to use your words and explain them in full.
Any character can only use the rules for a single race. But generally it's fine to narrate that you have other races in your ancestry if you want.
For example, if someone came to me and said: "my character is one-quarter elf, one-quarter human, one-quarter gnome, one-eighth orc, and one-eighth dwarf", I'd ask them to choose a single race to use the rules for. So they might choose to use the rules for their human heritage, and then they'd get the human's extra feat and skill points, but they wouldn't get the elf's meditation or the orc's darkvision or the dwarf's stonecunning.
This character could still describe their appearance the way they wanted -- maybe they'd look mostly human, but a bit sturdier because of their dwarven ancestry, and they might have pointy ears because of their elven ancestry, et cetera.
There was a feat in 3.5 that you could take that added a race to your own as kind of a template, say you was a gnome and when you took the feat you selected Goliath, you would qualify for prc, feats, and racial substitute class levels and all that, but if a spell or a weapon with bane or anything that targeted the 2nd race it would affect you just the same... I don't remember the name of it but I was going to use it to make a human warrior/spelltheif /master thrower/whisperknife