If your fish are recovering from sickness, then all you need is feed them more.
Have you tried to feed them beef heart?
You can get them from a butcher shop. Trim all the fat, then cut them into thin pieces form like blood worms. Feed them 2-3 times/day, they'll recover in 2-3 weeks.
The best looking one in my opinion is the blue sapphire, good shape, nice color.
The skinniest one is the ring leopard.
Your white and orange fish looks like a carnation PB.
If you can get some black worms, either live, frozen or freeze dried, get them. They'll go nut fighting for them. They all get fat after a month, warranty ...

How often do you do WC, and how much in volume?