Sharing a room: I recently moved my 2 oldest into the same room. 🛏🛏
Here are the ways I made it work:

They should be as close in age as possible. This makes it easier as they will have a similar bedtime routine.
It is preferable if they already have similar sleeping environments. Some kids like a noise machine, some want a night light, some want it pitch black, some kids like talking to themselves before sleep etc. Before combining my kids I knew that my daughter liked a white noise machine & my son no longer needed/wanted it. So what I did was over time turned the volume lower on my daughters. The @IQair luckily is loud enough that it works as a white noise machine- love the IQ air! (use my discount code DRORGANICMOMMY for $50 off)
I put my kids in a bunk bed. That said it is not recommended to have a child on the top bunk until they are at least 6 years old. I personally felt comfortable with my son at the age of 5.5 though. If your bunk bed is not covered, make sure to have bars.
Let’s talk about night time chatter & getting out of bed. Consistency is key. Do not cave otherwise your children will see right through you and it could be a nightmare. Chatter is expected and frankly adorable. I love hearing what my kids have to say to each other. I am personally ok with them talking to each other before bed. That said if it goes on past an hour, I walk in and quietly but firmly say: It is now time to sleep. Lay flat as a pancake, be still as a stone and quiet as a mouse. Visual language can help children. If one is keeping the other one up (which happened to me), I think it is important to let the children work it out but I offer guidance by saying: " I hear you, you are safe or it is time to rest.”
Finally getting out of bed - it is best to anticipate this by letting them know that “before I leave the room, is there anything you need to tell me.” (Or 1 last hug etc)

Do your kids share a room?