I have a question my boyfriend co signed on a car for a girl and his name is on the title as well as hers, she wants the car back but she had tempered with the temp tags and wrote a bad check to the dmv. Now she is wanting the car back, and she is willing to take him to court. Is he financially responible for paying her every payment she has paid and the taxes on the car? I'm worried that the loan company will come after my car that he cosigned for and our house, can they do that? Can we make her buy out his part of the car if she wants it back?

This shouldn't be under Real Estate Law. {Moved-<>}
A co-signer is 100% responsible for a loan. If he is also on the title, he is 100% responsible for taxes too. The other signer is 100% responsible as well, for both. Loan companies don't go after each person for half, they hold both parties 100% liable, and how you sort it between you is private. If she sues him, he countersues (this is where it's confusing about who owes how much).

As it stands both parties are to have equal access to the car, regardless of who paid how much.

Tampering with tags and check kiting are criminal matters apart from the legalities of the loan.

Car loans are never given for more than the value of the car, so they simply repo the car when it's in arrears.

She wants him to pay for everything that she has paid if we finance the car and we keep it including the taxes but that's double dipping isn't it since we would have to pay taxes on it too. And also if he take his name off the loan will his credit be ruined?

First, he can't take his name off the loan. The lender won't allow it. If the loan goes delinquent, it will affect his credit as a co-signer.

If his name is on the title, even along with hers, and he has possession, then let her sue him. If he can prove that she hasn't been making the payments, forcing him to do so to protect his credit, then he may be able to get her off the title. In this case, he probably would be required to buy her out by reimbursing her for anything she can prove she paid.

If he doesn't pay and the car is repoed, generally it will be sold at auction probably for less than the balance of the loan. He will then be responsible for that balance and they can go after assets that he is listed as an owner of.

Your information is too sketchy to be really helpful about who would owe whom what on a buyout. If she got some use of the car, she should be expected to have paid the payments during that time. Courts don't have the time or inclination to decide who used the car what month, but if it does go to court, be well prepared and organized or the judge will just get fed up and make an arbitrary decision.

When I said loan companies go after both parties equally, I don't mean they want double. They get whoever they can get to pay whatever is owed and then stop. No double dipping.

He and she should work it out or you all lose.

... I'm worried that the loan company will come after my car that he cosigned for and our house, can they do that? ...

As to your car: is he on the title? If there is equity, and assuming there is a deficiency on the other car, and they bother to get a judgment against him, possible, but not likely. There is an automobile exemtion in most states.

Who owns the house? If it is in his name, and he owns it free and clear, again, it is possible but not likely. There is a homestead exemption in most states.