J.A.
I have three girls and two of them share a room. My oldest had just turned 3 when my youngest was born. Even though they were in the same room, my oldest did not wake up everytime my youngest did. After the first few night, she would see me come in to get Victoria and just say "Mom she is crying" then she would go back to sleep. Chances are if he is not waking her up now when he cries, he won't wake her up if you move them into the same room. The first few weeks she might if she is a light sleeper, but just be consistant on how you handle her and she will get the idea that when her brother wakes up does not mean the whole house is waking up.