B & F have shared a room since they were 3 and 5. Not too far off from yours. Does this mean Steven's room will be trundled underneath Hannah's? My recommendation is to go to great lengths to make it "their" room, not just Steven moving into Hannah's room. When B moved into F's room, I found coordinating comforters (one in blue/green and one in pink/yellow). Then I allowed B to redecorate her "half" of the room, we put up those vinyl stick-em fairies and moved some of her stuffed animals in. F got to change around his room a bit to accomodate her.
As for bedtimes, now is as good a time as any to get them on the same schedule. You'll need to start getting Hannah to bed earlier if she's starting kindergarten in a year anyway. I'd just cold turkey start a bedtime routine that gets them both to bed at the same time. Usually if one wakes earlier, you can get them out without waking the other. Getting one to bed after the other is a bit harder
IMO.
I could go on, but I don't want to bore you! Bottom line, it was easier than I thought it would be!