We're moving house in a few weeks, and I'm worried about our cat getting confused/upset
We're moving literally 20 yards; across the road and down a bit. He'll still be pretty much on top of his current 'patch' (we are quite countrified, house adjoins fields of cows and a bowling green) but will have to find his way to it by crossing unfamiliar territory.
I'm worried that he'll just go back to the old house and be confused when it's not us living in it/the flap is blocked up. Also, our buyers are allergic to cats!
When I moved I was advised to keep cat shut inside the new house for a week to help them get familiar with it before letting outside.
My move was further though so I can see your problem about him going back to the old house.
At least if you keep him in for a while he will get used to where you are and where his food is now served. I can't imagine he will be made welcome/let in when he visits the old house given that they have an allergy so hopefully he will get the message.