i'd think twice about this. might have issues getting everyone on the same page. also a risk if one person goes bankrupt or has financial issues - it impacts everyone.
This one.
If your parents wanted to own DVC, wouldn't they own it by now? How old is your brother, is he settled, married, kids? Is he on board. Are you married with kids? Do you intend to be.
Lets just say for instance that neither you or your brother are currently married. Five years from now, one or the other of you are married and have three adorable and wonderful children - you no longer fit in a studio and need a bigger allocation of points - what do you do? Do you split the points.
Lets say neither of you is married, but one of you gets married and their wife really isn't into Disney - but introduced her spouse to the wonder of skiing - suddenly that brother - and his wife - aren't going to use points and wants out - do you sell the whole contract (you can't sell out part) or do your parents and you eat the cost of the contract.
Sometimes people buy with other people and it works out great, but make sure that everyone is on the same page about the commitment, that you understand up front how you are going to split the use of points and the expenses, and what you are going to do as the makeup of your family changes with marriage, kids, retirement - even - but hopefully not - divorce or death.