We're doing it right now with two kids. My kiddos are 23 and 5 months. I set up a play kitchen/toy area for my older baby in the...well, what used to be the dining room. She didn't like learning to be quiet during the little one's naptime, but she's adjusting just fine. I make a point of being really, really involved with her. For example, we go out to play just the two of us (plus the dog) in the backyard during the morning nap. Previously during the afternoon nap, we'd curl up and watch a cartoon because it's too darn hot to be outside, or draw, or she'd help with a chore or getting dinner ready.
But now, over the last month, maybe even two she's gone back to taking an afternoon nap WITH her sister. It's wonderful.
The girls also both sleep much better at night now that they're together in the same room. IF one doesn't go down easily, we'll put the baby in our bed until they both get to sleep.
Yes, I know we have two and not three, but the kids sharing a room has been frustrating at time, but mostly amazing. The girls are really bonding. In fact, today and yesterday, the baby had no smiles for me when she woke up from her nap but lit up for her sister. It's hard to be jealous when the baby reaches for a kiss from her big sis. So sweet! I'm really glad we did it, even if my MIL thought I was crazy. :-D
Congratulations, by the way!