Toddler and baby sharing a room

I would love some advice from parents who have done this already - the good and the bad stories please!

I’m planning to put my baby when she turns 6 months - if she is sleeping through the night at this point - in with her 2 year old sister who sleeps great, and goes down unassisted- again I’m basing this idea on the baby being able to go off to sleep unassisted at this point too. They will both be in cots, will this work?! Will they be able to go off in the same room or will they bother each other and make the whole situation a nightmare? No experience on this so just hoping for some advice please🙏