I have four smaller contracts with the same UY at the same resort. They are all listed under the same membership number. Each additional contract has a number ending in xxxxx.1, xxxxx.2 and so on. The points are all lumped together on the website. Depending on how many points are needed for a reservation, the first account is used, then the next account, and so on. If there are not enough points to finish a one day stay, a few points will come out of the next contract to complete that day.
With different UY's you cannot combine fractional shares of points to complete a one night stay. I also have another contract with a different UY but at the same resort. I sometimes transfer those points to my first contract to complete a reservation. In this case, however, I must be within the seven month window on the other membership UY as points retain their UY status when transferred.