It's been a while, but thought I'd provide an update! Had a chat with DH after all of your great advice. We decided we'd add on when we were ready, but not because of this trip. So paused that. And decided we would use our points as much as we could to help others out, but they'd be responsible for covering the cost of additional points/cash needed and would need to reimburse us at the rental rate if they backed out and we couldn't get our points rented out.
Since we were looking at trying to make this happen for July 2022, I was getting a wee panicked in November when no real decisions had been made. After all, if our points weren't going to be used for this, I have a LOT of other trips I'd like to be booking! Once I got some dates from everyone, I started pricing things out (had some help from someone at a rental store to figure out how far our points could go and additional costs). Shared that info with the family, not much response. Started looking at flight costs and yeah, no.
There was a lot of back and forth, some ugly things were said ("Then you shouldn't have had all them kids!" from one SIL to us as if we should have had this trip in mind 18 years ago), and ta da, Hawaii is not happening! Other options were offered, including HH and VB, but as of this moment no one has made any more movement on planning at all.
We already decided to bank some points, put in a few wait lists for us and "all them kids" to see if we can grab a lowkey vacation in June, and I am at peace.
(and we just got the email that our AKV resale contract just passed ROFR, so it looks like I'll have some more points to play with after all!)