No you can not
Yes.
Yes.
can a collection agency garnish your wages in texas
YES
Yes.
Unless you have a specific repayment plan that the collection agency agreed to, there is no legal reason that cannot sue the cosigner.
yes
If you are not refusing to pay and you pay the debt, they would have no reason to sue you. If you refuse to pay a valid debt, they may advise their client to sue you depending on what state you are in and what the laws are there. Some states only allow original creditors to sue and not the collection agency.
yes
Yes - they can, or they can put a lien on the vehicle.
If they've sold your case to a collection agency, they have been "paid" for your debt with the money the collection agency gave them for your case, so, no, they can't legally sue you - as far as I know.