Will is valid
2) Registration of will is optional
3) it is sufficient if will is attested by 2 witnesses
4) apply for probate of father will
5) enclose affidavit of one of the attesting witnesses
6) notice would be issued to your sister
7) if she does not contest you would get probate
8) if sister contests it would be converted into testamentary suit
9) you have to prove that will was executed by your father