I'm not a long-term expert, but hopefully I can provide an explantation that will be helpful and others can add info. We have points at AKV and VGC with the same use year. At the 11 month mark I can make a reservation at VGC with VGC points or at AKV with AKV points (but not at VGC with AKV points or at AKV with VGC points). At or after the 7 month mark I can combine points from both contracts to try to make a reservation at any of the resorts.
The same is true for banked and borrowed points - they can only be used at the home resort they belong to at the 11 month mark, but can be used at any resort on or after the 7 month mark.
Hope that gives you a basic understanding, I will let someone else add what happens when the contracts are at different resorts with different use years since I am not as familiar with this.