When did you start putting baby bits up

Ok so, 3rd baby once it’s outgrown the swinging crib, will be sharing a room with its stepsisters for 3/4 days a week, now my beautiful step daughters I’ve been in their lives since the youngest was 5 months, she’s now 3 1/2 so we recently moved into our own property and obviously set up the biggest room for the girls, now we’ve found out that we’re expecting baby will be in there too,

Now their mother has just had a baby and apparently she’s been having problems with the girls understanding the baby and they’ve been fighting, screaming etc to the point they’ve been put on time out a lot, I don’t want that to happen here and the girls was actually the ones that told me I was pregnant!

I was just wondering if you had siblings share when did you start Incorporating baby’s bits into the bedroom, I want to do it so they could help me put bits together and make them so they know they are still priority as well and not being left behind?

Sorry for the long post