dont get the tang, it gets to big. dont add any more clowns as they will be agressive towards each other. the two damsels are fine but i wouldnt add anything else other then those and the 2 clowns you already have, thats a lot of fish for a 12 gallon tank already. i only have 1 in my 10 gallon and im fully stocked.
in the filter you should take out the piece of filter material and just add a bag of carbon, also i would take out the biowheel.
you should add more live rock, add until your tank is almost full of it. like 4 inch from the top and like 4 inches wide at least
3 damsels in a 5 gallon wont work at all. they will become to big and the tank will crash because of to much bioload. i wouldnt do any fish in a 5 gallon and just have corals and a shrimp.
you need to get a CUC clean up crew. add hermits and snails to both of your tanks as soon as possible, or else you will have algea everywhere and all the nitrates will spike.
If i was you i would transfer all in the 5 gallon to the 12 gallon and focus on one tank for now because you still have a lot to learn.
Also if your lfs is telling you all these things are ok in your tank, please dont listen to them, come ask us first because they are there for money, we are here to help. sure some of the fish would work, but you cant have all those fish in 1 tank, way to much. i wouldnt put 3 fish of any kind in a tank under 20 gallons personaly, but id say the max for a 12 gallon is 2-4.
Please dont take this as an insult i just want to make sure you dont do the wrong thing because i hate to see people quit because its "to much work", when in reallity if you set it up right all you gotta do is some cleaning and feeding. i spend maybe 2 min a day on 1 saltwater and 2 freshwater tanks, and like 1 hr on saturday for cleaning and water changes.