I am not here to criticize .. you are offering a home to these chi guys which I appreciate.
We also hve 4 chis, 3 boys and one girl. Two of my boys are 13, and 12 years old. The young male is only 6 months, so of course my older guys have little patience with the fact the puppy is always in "play" mode. Fortunately, our girl who is 7 years old has a lot of patience with him. When she does tire of his antics, she will get stern and put him in his place.. then he will usually get in one of the dog beds and take a much needed nap. We do not interfere with her discipline of the pup. She is not trying to hurt him and he does not come back at her. (I think this is due to the male/female relationship.)
Now as to my older boys, the 13 year old has a heart murmur and takes meds for his heart. Naturally, we don't want him upset or fighting at all. He is neutered which takes aggressiveness down a notch. He will give the pup a stern growl to go away and we make certain the little guy complies. They are only in the room together when we are home. If we go out, Neko (13 yr. old) is put in our bedroom which he loves as he naps alot at his age.
Our 12 year old, Buster, is blind
and is also neutered. Mick (the baby) is aware that Buster (12 yr. old) is different.
Mick really does not pester Buster very much, but if he does get on Buster's nerves then he gets a stern growl and again we make certain the pup backs off. We are comfortable leaving Buster out with Mick and Snow (our girl) when we go out. Buster also naps alot at his age, and Snow and Mick usually curl up together separate from Buster. (We have 5 doggie beds in our living area, so Buster has no problem napping away from the baby.)
Mick will be 7 months old on June 2nd, and we will be having him neutered then (the age our vet recommends for this procedure), and I feel this will reduce his hormones considerably which will improve the relationships with the two old males also.
I think the suggestion of a couple of Iris Pens for you boys may be a viable solution for you. Two in the pens, and one out.. then rotate them so all get the same amount of freedom. Perhaps seeing each other, but unable to make contact to fight will allow them to become more tolerant.
Also, I am assuming all your males are neutered, if not.. that would be something I would have done immediately to help with the aggression towards one another.
Best of luck from my house to yours..