Are you feeding canned salmon and tuna or fresh? If canned, then all I would say is make sure you get the fish canned in spring water, rather than brine or oil. It sounds like a pretty good diet, and if your cats are eating all of the fish if canned i.e. the little crunchy bones too - then they should be getting enough calcium, although you might want to ask your vet about whether there is a need to maybe add some extra, especially as they are growing cats.
The only other thing I would think about adding is taurine, which is essential for cats. it is in all meats, but if the chicken and any other meats are cooked or in any way, processed i.e. minced - taurine is depleted, so it would be worth adding some. Its readily available online, in tubs of the powder, or powder in caplets - but make sure you find one that doesnt have lots of other ingredients in it - many do. You can just sprinkle it on the food and it appears to be tasteless, because my lot don't notice it!
Its great you've found foods that suit your cat - loads better than cat food!