Don't you have a copy of your father's bay form or your chacha's? It at least clearly shows name, family name and date of birth.RedShot82 said:
Also i have seen at least one case (my father's bay form) where my father was the head of the family and we lived in kind of joint family at that time so that bay form (dated around early 80's) listed my chacha (because he lived with us), father, dadi as well as my mother, brother and sisters.
Just try to verify this. You might have your chacha's name on the same document as your father OR you could get both of their B forms showing same parents.
One more thing, if your father is not alive today, there must be a 'reporting person' written on his death certificate. I have the one for my father, and my elder brother was the applicant. So the death certificate says "applicant name: <my brother's name>" and in relationship to deceased (son).
Is it possible that you chacha might be the applicant? since that is often the case. Or may be you could think of some other document which shows this.