Only the deed of sale or gareement for dsale is reuiredto be registered .
The buyer of a proeprty need not for registration of other agreements, if any.
Form your query the nature of agreement as mentioned by you is not clear and hence I cannot say for sure which one of these 3 is required to be registered.
Make one sale agreement and then register it.
Another alternative is to make a deed of conveyance ad get is registered.