I also have the kids separated, and then have some sort of "neutral" noise going on. I find that turning on the bathroom fan in that hallway, then leaving the door to the bathroom open, helps them all sleep better!
We do what it takes, right? Is it possible to separate him a little more?
For me, as long as they are not shrieking, and are still "resting" in the nap area, I am fine with them chittering away to themselves. My little part time guy tells himself stories. "And then Bxxxx see da dinosaur....Rawwwrrr r says the dinosaur". It's hilarious!