'Buyer Beware' is applicable in proeprty deals.
You should have consulted before paying token advance and signing agreement to sell.
ClassI legal heirs of deceased Hindu male are;Mother,wife,sons,daughters.
Death certificate, legal heir certificate/succession certificate are requisites.
The inheritance is to be recorded/mutated by authority under whose jurisdiction property falls.
All legal hiers should sign th sale deed.
Hence check with authority.
Let a very able counsel examine mutation record, chain, title etc etc and opine finally and draft the agreement to sell and sale deed for your long term interest.