Deed of sale or contract to sell?

Hi good day po my sister who is in the US own a house and lot in cavite she decided to sell the property but currently the property is not fully paid there is still xxxx amount balance to the developer. There is an interested buyer who is in Canada but she is asking his son to negotiate with me. My question is what documents do we need for both of us (me and the son) in order that the negotiation will be valid? What contract do we need to execute is it deed of absolute sale or contract to sell? By the way the buyer just want to pay us xxx amount and then he will continue the balance to the developer. Thanks for your help. More power and God Bless.

you should first ask the developer what their policy is regarding transfer of rights and what docs they will ask for to allow you to transfer on their behalf. also check your contract with the developer what it says about transferring the property.