Buying flat from land owner share

Dear Sir, I am planning to buy a flat from land owner share. This apartment has 58% developer share and 42% land owner's share. There are 4 land owners. The Agreement mentions the name of only one of the Landowner along with her daughter while the other 3 Landowners alongwith the Developer are not party to the Agreement There is a registered sharing agreement that talk about number of flats owned by land owner and number of flats owned by builder.Separate flat number distribution to these 4 land owners are mentioned alongwith UDS fallen to the share of Owners My local lawyer asked me to get the PoA from other three land owners and that has to be registered or they should be part of the Sale Deed alongwith the Developer Lawyers Comment: "In the Draft Agreement given only Smt. R. Shailaja & Ms.Jayadeepa, D/o Shailaja are Vendors/Sellers and Sri. Babu Reddy, Sri Bhaskar Reddy & Smt. Veena(other co-owners) and Developer M/s. Sumadhura Infracon Pvt. Ltd are not parties to the agreement and i am told that even in the Sale Deed they are not joining in execution of sale deed relying on sharing agreement. As properties are amalgamated, joint Khatha is there, I am of the opinion only on execution of sale deed by all co-owners valid title passes on, hence not recommended for purchase" Please advice. I really need your help or guide me on this.