We only have 2 bedrooms in our house and our kids (girl almost 6 & boy 2 1/2) have shared since he was 6 weeks old. (We moved him from the basinet to his crib.) We did our routine a bit different since I was nursing him. We'd do baths, brush teeth, read stories, have prayers, and then tuck her in. I'd then take the baby in the family room & nurse him once more. Then, while he was still awake, I'd put him in his crib. She was still napping for the first 8 or so months of his life. I'd put them down for a nap (his afternoon nap) at the same time. She'd wake up after an hour or so, come out & quietly close the door. He'd wake up after another hour or so had passed. Once he was 15 months & I wasn't nursing, we'd do the same routine, except that we'd rock with him for about 15-20 minutes before putting him in his crib (still awake). That would give my daughter time to relax & fall asleep before we put him in. After he turned 2, we do the same bedtime routine (still bathing together), except that now we put them down at the same time. Sometimes they stay up chatting & giggling, but for the most part, she falls asleep within 10 minutes, and he's out in about 20 minutes. We're going to get bunkbeds when he turns 3 (knock on wood, he hasn't tried to climb out of his crib yet!). I'd do seperate beds since I'm not too fond of changing sheets on bunkbeds, but there's no room for 2 twin beds in their room. I've asked my daughter numerous times if she wants her own room (someday we'll move into a bigger house), but her answer is always a very firm "NO!" ** I've thought of recording that on video and showing it to her someday when she thinks her little bro is a pain. :-) ** They love sharing a room. So far it has worked out fabulous for our family.
Keep the routines as close to the same as you can. Kids thrive on routines. I think it makes them feel safer & more content when they know what is coming next. Oh, and we don't give the kids baths every night. We have REALLY hard water, and our kids have pretty dry skin, so baths every other night work well for us (unless it is summer & they've been playing in the sandbox, or getting really dirty.) It will get easier for baths when your daughter gets older & can "play" more in the bath with her brother. Good luck!
Shellie