I did it, we had 4 of us in the same room right from day one. The girls were in top of each other as well so it was nice and cosy
Keira wouldn't have been that much older than Daniel either
It worked really well, apart from maybe the first few weeks where Keira was so excited everytime her baby sister woke she just wanted to see her. We were all pretty tired the first few weeks, and it maybe made things a little harder with a tired toddler. I think after a few weeks the novelty had worn off and she was so tired she would sleep through everything. They both became very good at sleeping through other noises and movement in the room and still are.
I don't think we let Maddi cry as much at night, I would usually feed her to sleep and she may have had a wee grizzle before she dozed off, thankfully she was an alright sleeper.
They are still sharing now (thankfully not with us anymore though
) and they still sleep pretty well. They do like to play a wee bit some nights and mornings.. well as soon as one is up...
The biggest problem I had was getting them to have day sleeps, I just can not get them to sleep during the day in the same room. Keira was always a shocking sleeper and had dropped her day sleeps well before Maddi was born, but it was occasionally was a problem when Keira really needed a sleep (now if she ever needs a sleep she will go in our room).
Kids are pretty adaptable so it can definately be done with out too much of a problem. Good luck!