One of our cats is 5 and the other 2 (sisters) are about to turn 3 so they were adults when we got Jax. We had a different dog (who passed in the fall of 2019) at the time the cats were adopted, an older greyhound who ignored the cats. In between our greyhound and Jax, we tried to rescue a 1.5 year old white GSD who had previously been attacked by other dogs in her house (multiple times). We thought it would be OK since the GSD had been raised with a cat, but, because of her attacks, she was fearful and lashed out at all small moving things, including children, so we could not keep her. I think this situation traumatized our cats.
There has always been some conflict. Jax has never learned to respect their space. He does not seem to recognize their cues that they do not want to play or that they want to be left alone.
The only change (other than Jax maturing) I can think of in the last 2 months was that Jax was neutered. 2 of our cats and Jax are now on medications to try to keep things calm but we are continuing to have issues.
The cats have been corrected with a water bottle if they are attacking him for no reason. (One of the cats used to stalk him and attack when he wasn't looking.) With the medication and water, he has not been attacked for several months. We have been working with a trainer since Jax was 6 months. As a result, we use a prong collar. So his corrections are a "Ah" with a snap of the fingers and a quick snap of the prong collar, with us standing over him and waiting until he lays down and is calm.
The 2 sister cats have been avoiding Jax lately but the sight of them, even walking slowly in a different room, sets him off. It seems to be mostly at night. The cats have a large cat tree, a cat shelf high on a wall, and the bonus room upstairs with a devise that allows only the cats to enter. The other cat has no fear and will walk up to Jax and sit inches from his face.
Jax is walked twice a day ( 2 miles each time) and either played with outside or taken to the dog park (weather-permitting).