Bully Cat

I have a three cat household. A 10 year old siamese male (Damien), a 5 year old DLH (part maine coon?) male (Orangie) and an approx 10 month old siamese male (Eli). All are neutered. When I brought Eli home I was a little worried that Orangie might play a little rough with him as he is quite large and wasn't always gentle when I had foster kittens. Boy was I wrong! I got Eli at 6 weeks, I was already his third home so I suspect he was taken from his mom too early. The lady I got him from said her older cat was beating him up, though now I'm not sure if that was true. From the day he came home this tiny little thing started bullying my large maine coon type cat! I've always corrected it as I realized from day 1 that this was very concerning behavior. I use a spray bottle and sometimes he does get a spanking when he won't respond. I was hoping when he was neutered that he would chill out a little bit, but he is still pretty much the same. It doesn't happen all day, but they have their energetic bursts in the morning and at night and that is when it is the worst. Whenever Orangie moves, scratches the post, meows, Eli seems to fixate on him. They don't fight enough to draw blood, or become injured but sometimes Orangie does yelp. They can eat together, and sleep together but when they are active during the day Eli will attack.
Currently I'm home during most of the day, but I'm going to be returning to work and I'm worried that for a few hours during the morning Eli will be harassing Orangie. Should I separate one into a room while I'm at work?

I think it would be a good idea to keep the new kitten in a separate room. just made sure there are no cords plugged in that the kitten could chew on and items he could knock over and get hurt . Also be sure leave a some water ,food and a littler box.