Well, I hate to be rude but there is always a choice. Your kids do not have to sleep in the same room. One of them might have to sleep on the floor of the living room, or the floor of your bedroom, but there is always a choice. And a less-than-desirable choice might be the best thing. Let them take turns sleeping in bed then sleeping on the floor. I'm sure they'll think it's great fun for a while, but after a few days it will lose it's charm.
OR...you could drag a chair and a book into their room and sit and read while they fell asleep. Any talking would be "shh"ed. Yeah, that would be rough on you but it would get your point across that you are not accepting the behavior.
If you have a newborn, then it is likely that they are having some issues with that. Nine years of being the center of your world is a long time, and now this one, single little being comes and gets all of your undivided attention. This smacks of 2 kids screaming out for attention. Couple that with the fact that twins have a special bond all their own, and it makes perfect sense that they're doing this.
You are the grown up. Are you going to get them to age 15 and say, "Well, we've tried everything and they're still sneaking beer?" or something? Like it or not, we are the parents...our kids didn't ask to get born. So just like you have to get up and feed a newborn, you have to get up and deal with this.
I don't mean to be unkind, but they're just kids. They want the boundaries. They want and need to be told "this is enough" and they need you to show them that you care enough to give up a good night's sleep to make sure they follow through. (edited to add: Ten o'clock sounds like a priveledge that can be taken away. Start bedtime at 8 and let them know that if they're not asleep by 9 you'll start bedtime the next night at 7:30. They may be overtired from all the summer activities. Once my DD gets overtired it takes a long time for her to settle and sleep.)
Good luck.