I'd happily keep DS2 in beside me for ages, but he'll have to get kicked out when i go back to work as I'll be doing shifts and tramping about early and late.
I'll probably have to move him a few weeks before i go back, so he'll be about 6 months old.
I'm getting a bit nervous about how it'll all work, DS1 (3 years old) is a great sleeper once he's asleep, but i just don't know how he'll be affected by his little brother being up a couple of times a night at least.
I have DS1 who is 21 months and also a great sleeper and I have recently moved DS2 who is 16 weeks into his room and there have been no problems at all. DS2 was waking once a night for the first few days they were in together and it didn't disturb DS1, he either slept through it or opened his eyes when I went in to get DS2 before going straight back to sleep. It was much more straightforward than I thought it would be!
I have DD1 2.6 and DD2 6 months I want them to share a room eventually but I'm not going to attempt it till DD2 is quite a lot older as I don't think it's safe. Don't get me wrong DD1 is lovely with her sister but she is only young and I wouldn't risk the remote possibility of her throwing something in the cot like a pillow or blanket that could go over baby or a heavy book or small toy. I don't leave them alone together through the day and wouldnt at night. That's just my view though.
Ds2 was 7months and a terrible settler/sleeper when I moved him in with ds1 - who had been through sleep training and was a perfect sleeper! Ds1 loved the company and slept through the night wakings, ds2 loved it and settled much better. Instead of complaining about going to bed, he used to lie in his cot giggling at ds1. They have had a great relationship since day 1 so it worked much better than I could have imagined.