Another positive experience here too...
DD1 and DD2 24 months apart and have been sharing a room since we chucked DD2 out of ours at 4.5 months!
We thought there would be major problems as DD1 needs a lot of sleep and DD2 is a very light sleeper who seems to survive with only 4 hours sleep a night some nights! DD2 is also prone to night tantrums and can scream very loudly for prolonged periods, DD1 has decided she is scared of the dark and has started to need a wee in the middle of the night. In short, there is a a lot of disruption!
They both seem to cope well, although after a very bad run of night tantrums from DD2, DD1 has taken to napping during the day again. DD1 was in her cot for the first few months, then we moved her out of it into her cotbed - we braced ourselves for much nocturnal baby prodding only to find there wasn't a problem. We told DD1 that she could have a big girl bed if she stayed in it all night!
We prepared DD1 before DD2 was born and told her she would be sharing her bedroom, we are also doing this in preparation for DC3 when DDs will move into a bunkbed - yes we are a bit cramped here.
In the mornings it is lovely to hear them chatting to each other, as soon as DD2 wakes up she calls for her sister. In the morning DD1 gives her any toys she requests and sometimes climbs inside the cot and goes to sleep with her - although she didn't do any of this when DD2 was young as she couldn't get in and was told not to and we kept toys out of reach (making sure DD1's bed teddy was newborn compatible just in case she handed it over in the night).
So yes, we thought it would be a disaster, when they are 12 and 14 it probably will be, but not yet