Age gap & sharing a bedroom

(Sorry if this is in the wrong spot in advance, couldn't find anything that more suited).

DD1 (3.5 yrs) has had a cot in her bedroom for the last 4 mths - to help get her used to the idea she'll be sharing the room with DD2 (now 3 mths). We've been talking about it etc though I'm not convinced DD1 is actaully aware of what is going to happen.

So I've just put DD2 down in the cot, and DD1 seemed to not like that one little bit and threw herself on her bed. DD1 then got into her bed and I made a big deal out of her sleeping in her bed like a big girl and showing DD2 how to do it etc. Managed to get DD1 out of the room, and then went in to check on DD2 and OMG - she is asleep!! YAY!

Then both DD1 and DS kept going into the room and hanging around the cot and just generally making a lot of noise, so I told them 'DD2 is sleeping and to be quiet' - which of course they didn't listen lol, so I took them both out of the room and closed the bedroom door....

I'm not sure if I've done the right thing though? I feel a bit mean keeping DD1 out of her room because DD2 is sleeping; though I want DD2 to get used to sleeping in the cot as she is rapidly growing out of the bassinette....

Help, tips, advice, anything PLEASE ;)?

Sleeping arrangements have always changed in this house. First we had dd1 and dd2 sharing, but dd1 kept waking dd2 at night. Then we had DS and dd1 sharing, it was a bugger to get them down at night (they shared a double bed) then DS and dd2 shared, that didn't work, so now DS has a room on his own and dd1 and dd2 share the double bed. Dd3 is still in our room and probably stay there for a while yet.

We had the toys all out in the loungeroom so the only reason they went in their rooms was to sleep. Now they have some toys in their room but they mostly play in ds's room and since he doesn't have anyone sharing it works ok. Dd1 and dd2 nap together during the day and DS just floats around annoying me until they wake up lol

Our kids have always shared bedrooms. If one of them is sleeping in the bedroom, then the others are not allowed in until after they wake up. It is the only practical resolution. If they want something they get a chance to get it out before whoever goes to sleep, or they have to wait until they wake up. I believe it is actually a good way for them to learn how share and understand that sometimes you have to wait for things you want. :)

DD and DS share a room and it is only a recent thing. I moved his bed in there before he was ready to transition to it, just so that DD could get used to it. Like Mel no toys are in their room.
The first nigh she had a fit about actually having to share and did not want him in there despite his bed linen being on the bed lol. He came in with me about 4am that morning and at 6am we were woken by an angry 5yo wanting to know where her brother was and that I was to leave him there all night the following night!

She got better at leaving him alone while he slept, and he got better at sleeping through her noise. I did have to shut the door for a bit though.

All 3 of my girls share a room, so when dd3 is sleeping during the day then they arent alowed in. They only have books in their room, so generally if they do go into their rooms to play its for quiet time for reading.