Not about pregnancy, but about oldest child

So right now, I have a 7 year old boy, a 3 year old boy, and 25 weeks pregnant with another boy!

Our oldest is not listening to us when it comes to playing with or just using his imagination regarding guns. Just so everyone knows, we do not have real guns in the house, just toys.

Recently, he's gotten too morbid with his play, like going into detail with what he's doing to people with guns and making gun noises. He's obsessed, that's all he talks about.

I don't know how to stop this. It's affecting his summer park program. So much that if he doesn't stop, he's going to get thrown out.

I've taken away youtube (he just watches hobby kids- which I hate and lego war animation stuff), annoying orange show, and some others that I think are too much for him. I've also warned him that he could get kicked out of school for this behavior. Still not working, last night I took away his late bedtime. He really likes being able to stay up later than his brother.

Do you ladies have any advice? My husband doesn't approve of spankings or anything like that and really, I think he would be too old for that anyways.

I just need to get this resolved before school starts, otherwise he probably will get kicked out...

Thank you for all of your advise.