First, don't try to convince him that you are making a wise investment. Not an investment by any means, just a prepaid vacation BUT you still have to pay annual member fees that continue to go up.
Buying four smaller contracts makes it easier to sell them when you tire of it all or have financial difficulties. You'd have to purchase the first of those resale since the smallest you can get from Disney now is 100 points at AKV. You want to get the same UY for all four to make it easier to use those points. Even if you bank and borrow to get 150 every three years at a single resort, that probably wouldn't be enough for a good stay for a family of five.
You'd either have to use those points at 7 months out at the non-home resort or at 11 months out at a home resort and have to move between two resorts. If they are separate master contracts, you'd have to transfer between the contracts (only one per contract per year) to get more for a single stay.