Nope, it's not that easy to file joint tax. I guess you have to be a family member, either parents, children or spouse.

 About the instate tution fee..unless you are categorized as "Resident" you cannot get instate tution fee.

Even if you are "Resident" doesn't mean you will get instate tution fee. Most of the school in US requires a "Resident" to be in the same state, (school in which you are trying to get instate tution fee) for a year in order to qualify for instate tution fee.

Some of the colleges like mine requires to be in same area not only state, like someone in LA, CA couldn't get  instate tution fee in SFO school, in CA.

So, check out ! as I said its not that easy !

Sampada