Is this behavior okay?

[BryanJohnny]

I have a pair of sibling IRN's and they've been hand raised. Recently, they've been attacking each other by the beaks. I'm not sure if they're playing or fighting. They don't peck each other's feathers or anything. They just open their beaks and bite each other's beaks. They have no problem sharing the same food and water bowls or anything. Is this normal?