The program is for the owner and not the membership.....as long as an owner is eligible to purchase, they get all the benefits, regardless of what they own.
Just like I visited the lounge the other day to see the characters, even though I was staying on my RIV resale points. So, its all about the owner and not what is owned.
If you are
DVC Y, you can purchase it and unlock all the benefits. Now, if one has one UY, then both owners only makes sense if you want to unlock the BOGO points for trips in 2025 and 2026, and don't plan to pay for it in 2026....
But, for those of us with multiple UYs, we have the benefit of being able to access for multiple ones. We still can't get more than 24 total OTU points on any one membership, and still can only get BOGO free for a total of 24....but, it does give us a bit more flexibility.