When you buy your adult siblings will need to sign all documents relating to the sale. I’m assuming you’ll be paying cash but if not they’d be equally responsible for any loans secured by a mortgage on the property. They’ll be liable for dues and any special assessments.
Their financial issues can impact your
DVC contract - if a sibling divorced the contract would be an asset in the divorce proceedings, if a sibling declared bankruptcy the contract would be an asset in those proceedings, depending on how title is held it might also need to go through probate.
I’d hesitate to do this personally. The only benefit they’d not get IMO at the moment is discounted APs. The discounts on merchandise/food they can get via a Disney Chase credit card.
I do have my adult son on my membership, but I‘ve paid cash for all my contracts & thus was not subjecting him to additional debt, I knew I could easily pay the MFs as well so would not be subjecting him to those bills. I was fully aware of the possible issues that could arise when I went that route & I was very familiar w/ his financial situation & knew that if he ran into financial problems I’d be the one bailing him out anyway. For me it was one less headache for him when the time comes & as sole heir he has to probate my estate.