Can you provide more details.

So you bought a house that is REALLY close to your current place. When do you move out of your current place? I assume you have a overlap and are trying to figure out the best way to transition?

I would use your group as a decision factor. Some kids prefer that slow transition of seeing the new place for a bit before being fully submersed. Others would be better with a full out switch, BAM this is the new place, this is how it is now.

If given the option I would likely do as you mentioned. Drop off at old house, go for an outing to play at new house then back for nap and pick up at old place. Then slowly extend from there...drop off at new house but home for nap and pick up at old house, then drop off and pick up at new house (but nap at old house) then full day at old house (when you are set up for it).

One thing I would suggest is that as soon as it is final (inspection done etc) that you let your families know ASAP. Make sure they know you bought a new house and it is VERY CLOSE to current house so no change for drive time or anything. I would worry that they pick up on cues and think you are moving and they jump ship expecting you will move further away etc. All it takes is the kids mentioning you packing boxes or them seeing something in your house to tip them off. Tell them before they figure it out themselves!