I'm going to say this as well as I can without coming across as an asshole.

Why would it hurt? While I've never done it nor do I intend to do it, from when I have seen it in porn it just looks like opening your mouth really wide. I can see getting a jaw cramp from that, but as long as you don't do it for an extended period of time that shouldn't happen.

I don't think this is really all you're building it up in your head. It's not like you're going to be sucking them to completion while they are both in your mouth. At most it will probably be suck the seperatly pop them both in the go back to doing it seperatly again. I am assuming that you have never watched a porn where a woman has done this before.