I had exactly the same as you, four cats being terrified by my pup and they would not stand their ground and bop him.
I was really distressed about it and thought it would never ever get better. I also felt really guilty for the cats and thought I had ruined their lives.
I was wrong, they are now the best of friends and all is calm in the house.
The only way we could improve things was with a long line in the house at all times. It allows you to stop a persuit as soon as it starts by stamping on the lead and backed up with the leave it command she will eventually get the message. As the pup stops chasing, so the cats calm down and stop running.
It takes weeks I won't lie, but do not despair, it does get better as long as you are consistent and do something about it now.
I am afraid you can't just ignore it and let them get on with it or it will become a play behaviour your dog will continue with.
Have pateince and hang on in there. x
Ted on his long line when he was still a cat chaser
And now