Is tailgating still a problem though Sue?
We have successfully managed to keep little uns in till they've been spayed. It takes some effort though and there are occasions when the older ones had to either put up with staying in kitchen or had to suffer lock down with the young uns. No lasting damage
We have normal cat flap but you can set it on in only, out only, fully open or fully closed. They only problem we had was that Dinah learned how to lift flap towards her
Happily she is the mumcat and already spayed when she arrived with her two babies. I had no qualms at all about locking the youngsters in a room whilst we were out so that the older ones could come and go as they pleased. Left radio on though so they could listen to the news