It would be *possible* to do what you're proposing to do, but highly unlikely to find someone where this would work out perfectly given the restrictions on one transfer in/out per UY per membership.
If your contracts are in different Use Years (multiple memberships), and the person your transferring with has multiple memberships, then it's possible to make this happen all within one Use Year. That's IF you can find someone who is looking for the exact opposite trade as you, and don't need more points than you're willing to give from Resort B, etc. -- theoretically that person could be out there for you, but the likelihood of finding that is pretty much zero.
If your contracts are in the same Use Year, then you'd have to do a transfer in of Resort A points for 2026 and a transfer out of Resort B points for 2027 UY (eligible as soon as you are in your 2026 UY). Will probably be most possible if you do this with two different people, and pay for the transfer in, sell the transfer out. You could then bank your excess 2026 Resort B points to 2027.
There's also an option if you can find someone who has 2025 UY Resort A points to transfer in, as long as they haven't been banked yet, you could then bank them to 2026 -- you would just have to use them in 2026 as you plan, as you wouldn't be able to bank them again. You could then transfer out your excess 2026 Resort B points.
One other thing to note, you can transfer in a different UY month than you have for your Resort A points, but the points aren't commingled perfectly into your membership and they set up a temporary membership for those points. So there may be some issues trying to book a reservation using points across memberships like this. I think this has recently changed (I was just able to book a night combining points from transferred in May UY points and my own December UY points), but would always be best to find points that match your own UY, if possible.
I've gone through this whole process before and plan on doing it again in the future so happy to talk through specifics on how you can make it work if you want to DM me!