About 4 months, mine weren't bothered being near each other and 1 was waking the other
I separated at 6 months when they moved to their own room. They have their own sleep space now, which is good because they were getting really mobile, but the cots are next to each other and they often roll to sleep facing each other through the side of the cot 💕
we separated around 4-6 week old for this same reason, we put them in two separate next to me cribs as we found they was disturbing each other! i put little boy nearer to me and he settled better than i expected without her at the side of him x