If the property was on your father's name, then his brother who has no rights or interests in this property cannot grab this property for any reason.
Since your father is not mentally well, he cannot transfer the property to your name, even if you get one transferred to your name, it would be invalid when someone challenges the same mentioning that your father was mentally ill by producing the documentary evidences to substantiate his mental ill health and make the transfer invalid in the eyes of law.
The builder cannot transfer the property to your name if the property was on your father's name, in the give circumstances you may approach court with a petition to declare your father as mentally retarded person and to appoint you or anyone as court guardian to take care of him as well as his property. Thus in the given circumstances, the property will remain on your father's name alone till his lifetime.