Can i write a letter of permission to my mom to live in my house thaT was willed to me by my dad without a lawyer?

if the letter would make her happy then write it. no lawyer needed. in fact no letter needed since you are the owner. again, if the letter would make her happy... does the concept of whether it is legally binding really matter? now if you want a legally binding contract you can either buy one of the fill-in-the-blank forms, write one yourself from scratch or go see an attorney.