Helping sibling adjust?

I am due 7/1/18 with my first (a little boy!) and also have 2 step daughters (6 and 8), both of of which are very excited. However, yesterday they started saying that Daddy and I won’t have enough attention for them as the baby is going to need all of it. Our oldest said she’s read it in books etc. and the youngest said she heard it from her big sister.

We have kept them as involved with everything as possible including looking @ the baby stuff we have bought so far and looking at the registry.

What else can we do to help this be as easy of a transition as possible? They’re unfortunately losing part of their playroom for the nursery (we are just rearranging things) as we only have 3 bedrooms currently. We are doing a big sisters trip to Disney in April as one last hurrah before Owen arrives!