Personally, I would worry about this. We have a newborn, and one aged 4/5, one 8. All girls. Each of them is caring and considerate. However, the youngest just wants to cuddle her and kiss her all the time. To do this, she'll actually sometimes put her hand down and lean on the child. At the moment we're obviously allowing the close contact, but watching like hawks and trying to educate her that the baby is small, and cannot take any weight on her, that she shouldn't smother her with affection too much.
There's no way I would allow the baby, even up to 1 year old, in the same room at night, as kids simply do not know how very fragile a baby is and I cannot put my hand on my heart and say I know the 4 year old would not get up in the middle of the night and try and pick the baby up, cuddle her, etc. The actual thought if this is making me feel a bit ill, to be frank, and I am not prone to hyperbole. It worries me just thinking of it.
The 8 year old is wonderful with her, and obviously is intelligent enough to know how careful she has to be, but there's no way I would consider putting a baby/toddler with a 2 year old.
I'd advise you were very careful if you did, but it is not something I would ever consider, especially with what I have seen first hand. The very worst thing is that my middle one, just wants to love the new sister, and it's this love that could end up hurting her the most.