Ours don't wake each other often. Dd (4) is like her mother, and just rolls over and goes back to sleep if ds (2) manages to disturb her. That said, they are both free to come downstairs to us as soon as they wake (not usually before 6.30, often later than 7)
have you tried to leave dd2 and see if dd1 does wake up? I'm always surprised when ds2 (18 months) screams in the night and ds1 (3) doesn't even stir.
Have to admit though that if either of them wake up between 5 and 7 they just get put in our bed, as I refuse to get out of bed before 7! Is she waking earlier because its lighter?
We have this problem to an extent, but I'm afraid I don't have an easy solution. Ds's are 18 months and 3.5 and we actually abandoned two previous room sharing attempts because they were disturbing each other too much. A few months ago we tried again and it has been better.
Our main problem is that ds2 often wakes early (around 6) and liek you, we don't like to bring him in to us (he would just start larking around on the bed anyway). We find that he does wake ds1, but we have encouraged ds1 to ignore him as much as possible (he is to 'hide under the duvet cover and try to go back to sleep' -which he usually does - bless!)
Its not an ideal situation, and we've had a few grim mornings with them both screaming, and I do feel sorry for ds1, but I think the only thing for it is to try to behave as much as possible as you would do if they were in separate rooms - I'm sure you will find taht dd1 adapts to some extent. otherwise you will probably end up creating/maintaining the early waking problem for dd2.
Sorry, probably not much help, but I think you ahve to try and ride it out and hope it gets better. Or give up and try again in the autumn!
It is difficult. DS2 (2) is encouraged to get out of the room and into the playroom, where he messes around for an hour or so before DS1 (4)surfaces at about 7.30.
5am is a bit much though! Agree it might be better to try again in the Autumn?