Twins Mady and Cara Gosselin turn 9 this Thursday, and it looks like their birthday gift is going to be a public battle over custody on the big day. Jon Gosselin told ET Online (via PEOPLE) that his estranged wife Kate is trying to alter the existing custody arrangement to cut Jon out of the birthday festivities - and he's not having any of it. "She's trying to prevent me from seeing my kids on Mady and Cara's birthday," Jon says. "That's like giving her full custody by obeying her."