Three year old and 18 month old sleeping in same room

[PiperG]

I'd be really grateful for any advice on how to to make a smooth transition of moving my three year old DD and 18 month old DS into same room together at night. Have been mulling it for absolutely ages and am ready to do it now (and think they are too) but want to make sure I go about it in the right way so that we don't make a total pig's ear of it ... DD seems very happy in principle to share with her little brother, but both do wake occasionally at night, and DD always wakes earlier (6ish) and comes up into our bed, though DS doesn't wake till about 7.I'm not sure whether they will disturb each other a lot or whether they'll just adjust. Any advice very welcome!

Ours are together and it is great. They are the same age as yours.
They sleep through each others crying (although I have occasionally found dd1 sleeping with her hands over her ears!). dd1 often decamps into our bed during the night or early morning and has learnt to quietly shut the door behind her so dd2 doesn't wake.
We often hear them chatting together as they drift off to sleep. It's really sweet.