I Want To Be Liable If My Family Does A Fraud

My aunt bought a property in my fathers name but now she doesn't trust him so she wants to sell the property but my father is not allowing her and me too I don't want her to sell it as both my aunt's and ours property are connected and if she sells it we'll face some problems. So I just want to assure her and make an agreement that if my father sells her property without her permission and acquire it by false means then I will be responsible for it. I will be liable for my father's fraud and I will repay it.