It’s like you are two different owners. To use together, you have to transfer.
You are allowed only one per UY, in or out. Once transferred, points still have all the same rules and you may or may not see them on the dashboard.
If it’s an occasional situation, it can work. If it is regular, then it makes more sense to do what it said already. Book each part on its own and ask them to note it’s a continuous stay
They can’t merge reservations across memberships. We do this a lot and have yet to ever not been in the same room.