Theoretically the agent should have studied the seller's deed of sale before accepting the mandate for the property. In reality a lot of sellers are unable to produce the deed immediately (it may still be filed with the notary that handled the previous sale) and it sometimes takes a while to produce, but certainly the contract for sale should not have been signed if the sellers had not produced the deed. It looks like both the agent and the notary are at fault here. In any case, it would seem that the agent's mandate is worthless. I would hope that by now your agent has discovered the real situation re the wishes of the other sellers. If they are in favour of the sale, you may want to hang on even longer to get the property of your dreams. Otherwise, you should be able to negotiate something with your agent, bearing in mind that the agency is at fault, but that it would be better for all concerned to avoid litigation... Good luck!