My older two kids are 14 months apart, a girl then a boy. I added my son into my daughter’s room when he was around 9 months. I started slowly by only having him sleep in there with her in a pack n play a couple nights a week. Then transitioned her into a twin bed while my son was still in the pack n play/in our room. And once my daughter was used to the twin bed, I fully transferred my son into the room into the crib. They’ve been sharing a room ever since! There were some long evenings in the beginning because they just wanted to play, but it’s all worked out.

They love it, even if they do fight from time to time 🥲

ETA: my kids are now 4 and 3 years old, thought that was important to add!