S106 Agreements by executors - "Persons Interested in Land" - Public forum - Planning Advisory Service (PAS)

I have been asked to enter into a S106 agreement between the Council and the executors and Trustees of an estate. However I am having difficulty in getting guidance upon just how "interested in Land" under S106 (1) and (3) an Executor is, and if any S106 agreement entered into between the Council and Executors would be enforceable against a purchaser from the Executors. I would welcome any observations upon this from members of the forum. Lawrence Handy Wakefield MDC