Maybe. It depends on what their intent was in creating the joint account. If it's all mom's money, and she just put brother's name on the account so that he could write checks for her (a really bad idea that is way too popular) then the account should become part of her estate. However, the presumption is that her intent is that the joint owner be the sole owner of the account when she passes away it's just brother's money. The presumption can be overcome by evidence of her intent that it be in her estate, but nobody ever thinks about that, so there's never any evidence.
Answered on Nov 06th, 2013 at 11:34 PM