K.B.
I went through the same thing with my kids. I have three and they are all in the same room. We have two boys and a girl. I trained the boys to not come out of their room until their clock says 7. It works most of the time. It's worth the effort. Our little one is only going to be two, she doesn't get it yet. Your 3 year old should get it. I put mine together when Luke was 3, almost 4 and Isaac was 2. They are 16 months apart. We do the music too. I also have a fan going for white noise. It is aimed at the ceiling, not blowing on them. It works really well. When she was smaller and waking up at night, I would turn on the lullaby music and no one else would wake up. I really like having them all in one room. I have no toys in there, just beds and stuffed animals. They only sleep in there. I never did a baby gate, but the lock on the door too. Good luck! If I can help out anyway, let me know.