It truly is a deed of real property, just like your house. If his name is on it, he will be responsible for it. If the siblings decide to default on their share, his name will be on it and he'll be responsible. I would quickly have him remove his name.
My story:
My mother bought a timeshare back in the 80s. When she passed in 2001, I was the only one that had any interest in it (damn sentimental reasoning!), so we agreed that we would just deed it to me and I'd pay the maintenance fees and get use out of it. Well, now I really want to get rid of the thing, because I don't live anywhere near it and so I have to exchange it through RCI (another membership fee) and they charge me an additional $200 to use the exchange! So, I'm in for close to $1,000 in fees per year - Anyone want a FREE timeshare at Havasu Dunes in Arizona??!! I'm dead serious. I am willing to deed it over to anyone who will have some use for it... hell, I'll even pay 2013 dues.