This is going to sound like I am comparing a sibling to a cat which is not my intentions BBUUTT...
We have had a really good go with redirecting Wes with "You can't do XYZ but you CAN do ABC". Wes was having a rough time with the cats, and even tried to kick them (good times buddy....good times). We gave him a short and sweet "We do not hurt the cats. OUCH! Gentle/calm hands
(what we call the opposite of being aggressive with his hands - he doesn't hit, but he gets wild with them) with cats <insert example> then a redirection of the We can't kick kitties, but we CAN give them kisses <insert cat kiss>
He now tries to chase them down to kiss them

I have no idea what the "right" approach is, but since I get the impression Wes just flat out doesn't know that he is hurting something, or his action will physically harm something, showing him how to interact in a positive way has helped him. I know Wes understands a lot of what we say, but knowing that developmentally he doesn't quite get the whole empathy thing. I will just lead him to positive behaviors and we can work on an in depth "why" when he gets it.