My mother and her boyfriend of 25 years had a joint checking account in his and her name only. He past away and his kids and the estate want 1/2 of the funds. Also he never got divorced from his first wife. This is in the state of Wisconsin. Do the kids have any rights to the monies?

F the account was held as joint tenants with right of survivorship, then no, they have no rights to that money. If the account was held any other way it would be dependent on the wording of the joint ownership.

Yes it will all depend on exactly how the account was opened. In most joint accounts, if one dies, all of the money goes to the other.

Also since he is still legally married, unless there was a formal separation, the wife will have claim before his kids ( or a part claim)

But no normally this money will not go into probate.