All my kids (DD1 is five, and the twins are three) share a room. The girls have bunkbeds, and DS is across the room in a twin bed. It's a really big room, though, bigger than most people's living rooms. Anyway, we do have awful nights where they keep each other awake, and phases where they have trouble settling and get up to all kinds of mischief. I tolerate it to a point, actually, because I think that stuff is part of building the sibling bond. When it gets ridiculous, I go and sit in the corner of the room until they're asleep. Usually after a few days of those shenanigans, they cut it out for a long time. Often I do find them in each other's beds, when I go to check on them late at night. I'm fine with that.
I transitioned mine from cosleeping as young toddlers, between a year and sixteen months, gradually. So I'm not sure I'm much help about the transition. I do think, though, that it was easier to transition the twins than it was to transition DD1 alone. I think they made the transition more easily because they weren't expected to sleep ALONE the way my singleton was. They still had each other.
It can be rough during periods of illness. I keep a mattress under my bed to pull out for a sick kid, so that the others aren't kept awake. (We did once have a lovely issue related to one child vomiting on the other.) Bedwetting has also been an issue-- DD2 will tell you with fury about the time that DD1 wet HER bed.
But on the whole, I LOVE that they sleep together. I like to think of all the wonderful memories they'll have and the bond they'll build.
I plan on keeping them in the same room until the twins are old enough that it seems better for DS to have his own room separate from his sisters. I don't know when that'll be-- I figure I'll know when it's time, and then we'll have to find a way to get him his own room.
But for now, it works well.
me , he , my three , , and -- and the one we lost