Male cat likes to pounce on females all of a sudden?

For the past year I've noticed my previously sweet 8y/o neutered male likes to pounce on two of my female cats.  I usually hear hissing and screeching from the basement or another room to find him with his tail all poofy running around chasing one of the two females.  I asked a vet about it. She said to separate them, and reintroduce them. Did that, and it's not working.  He has hurt them by scratching them a few times. I don't think he means to hurt them purposely but it happens as the other cats swat at him, or he pounces on them. I've tried playing with him more. Giving him more attention. Nothing seems to work. I've tried calming treats at night especially. They seem to take the edge off of it, but he still does this.  I've noticed it got worse after my dominant male cat was diagnosed with Hyperthyroidism.   Since diagnosed I think he may be trying to become the dominant male.  I noticed when he plays with the other male that he gets a little more aggressive now too.  Not really sure what to do.  For the most part he's wonderfully nice and sweet. But he likes to chase the two females.  The other female will chase after him and pounce on him, and so he usually leaves her alone. 

Trying to find a solution. He's been into the vet, and she checked for a UTI. Sometimes that can cause behavior issues.  She thinks it's just a behavior issue and she's not sure what exactly is the cause.  

Any ideas?

Charlie my male cat who likes to pounce on the females is not the one with HT.  That is Smokie.  I did think about HT being that he likes to cry at night sometimes, and that he's a little more agressive. However I've been monitoring how much he has been eating/drinking and his weight.  They have not budged, and I think he's gained some weight since I last weighed him. So I don't think he has HT.   My thought is that it is from Smokie who I would deem the dominant male of the group, being sick. I think he senses it and it's stressing him out a little.  I will check out the link that you gave me.