My DS1 was 25 months (a little older i know) when DS2 was born. I too was very hesitant about the sleeping and disturbing one another as the bedrooms are so close. DS1 has always been an excellent sleeper and i stressed about nothing because he has slept through everything. When DS2 was 6 weeks he was in his own room and it worked fine for us. I would go to DS2 whenever he woke so as to not allow him to get too noisey and i would take him and feed in our bedroom. I can't think of a time when this has ever disturbed DS1. If they had happened to share a room i really don't see the situation being any different. That is night time though...

I'm imagining the situation in day time and that would have been a bit more challenging for us. In the day DS2 occasionaly requires a little more help to settle and every once in a while i hear DS1l call out to him to be quiet At least i could try and shut doors to quieten the noise. You could consider day sleeps (generaly a little warmer than night) being seperate for the first few months, if your LO agrees with this

Honestly you work with what you've got and your LO's will adjust to that fine, eventually they won't know any different. I found my DS1 adjusted really quickly to the arrival of his brother. Also in most cases you will probably find that you'll wake/attend to your newborns stiring before he/she gets to a real noisey cry when you have DS sleeping.

Sorry if this is a bit jumbled, i'm just writting my thoughts down as i type. Im sure everything will just fall into place for you with the sleeping arrangements