iI'm sorry this is happening to you, it must be very worrying. it dosen't make any difference practically. If you have defaulted on the loan, and your dad also cant pay it, it dosent matter if he is the main named person, or the garuntor, it will affect his credit standing either way as he will be deemed responsible for the loan with you. Being rushed and being pushed has nothing to do with it ... loans come with a cooling off period, wher you get a chance to think abut it cooly and logically within your own home, doing the maths if required away from the selling environment, so you cant use that as a reason not to pay
You need to look at the paperwork as you signed it, and it will tell you all the answers, including those i suspect you DO already know. If you are not looking for a loophole, what is the purpose of asking "do we have a leg to stand on"? in what manner do you mean?
i wuld imagine you will find you have signed paperwork making it all legal, wich you also would have had a chance to peruse at lesuire