My dd and dp's son have met, but he has ADHD and OCD and doesn't like change. My dd also has special needs (she is mentally impared). Both are only children, so have never had to share their home/parent...
Any suggestions on how to get both of our children used to the idea of sharing a home?
I think the key will be having them spend as much time together before the transition, and lots of communication about what's going to happen and why beforehand.
You say they've met. I'd probably have them on fun outings together, on neutral ground, to hopefully help them get comfortable with each other beforehand.