Execution of settlement deed

I am the only son and mom passed away. My dad has different properties, ancestral (got from his grandmother) on which i have given my money to construct a building by taking a housing loan, some properties he has acquired with his earnings in his name and my mom's name (who is no more), some properties which i bought in his name with my money (cash transferred through his bank a/c from mine). Currently he has come under influence of some outsiders and want to get married again at the age of 65 (obviously they are targeting the property that he holds). He has agreed to transfer all the property he has in my name. What is the best way to deal with this transaction and also in a way to avoid all legal hurdles going forward (due to the opportunists who are targeting our family) Also is there any risk that they might claim property share at a later date. On a very different note, what if he has already married someone without my knowledge. Do i have any course of action that i can take care of my hard earned money?