Father filed a fake cheating case against wife and son. How to defend?

Family : Father,Mother, Son. -->Father is not living with us. -->own a House on Father's name till 2004. --> In 2004, due to financial problems, father took money from Mother and had given the house to Mom & son (thru Govt. proceedings like registration etc.). Now the House is on the name of MOM & SON. --> Father has become Blind, due to some illness, carelessness. --> Father sent a Lawyer notice saying , taking advantage of his blindness, Mother & SON focibly has written the house on the name of MOTHER & son from him. --> In the Notice , Lawyer/Father is asking for the EXPLANATION of how can he cannot have the rights on the HOUSE? Questions : 1)what happens if we don't respond to the Notice? 2)If we respond how to respond, what is the process? 3) How much time does it takes to go to COURT after this notice? 4)How much MONEY that it takes for all this court proceedings?