Need legal or experienced advice for SRA project

First of all sorry if it’s under the wrong flair. My father started from chawl and we still own that house. Recently, a builder came for redevelopment, but there is lot of confusion. Some say builder don’t have all the required documents, some say all permission are there. Few have taken the rent for 6 months and now builder have started demolition process for them. He is also using pressure tactics and using random goons for it. My query is what all documents we should ask/ should know that builder have before we sign the agreement and handover our keys? P.S We don’t have problem to handover, only if builder have necessary documents