Looks like some serious bloat there, fast them for a day or two, don't do epsom salt right away, only if they are not showing any improvement. Epsom salt helps reduce bloat.
This may sound a bit odd, but feeding them peas helps reduce bloat and can also get rid of swim bladder.
Buy frozen peas, never buy peas that are not frozen. Put a pea in a cup, fill the cup halfway with tank water, put the cup in the microwave for 1 minute. Dump the water (Careful, the water will be very hot)
Take the skin out of the pea, NEVER feed them the skin, it will make it worse.
After you get rid of the skin, cut a small piece of the pea about the same size of a pellet. Feed your fish 1-2 small pieces. Wait 10 hours and you should see some improvement. I tried this with all my bettas and it works 100%.
WARNING: The peas sink to the bottom of the tank, so be careful.
Good luck, if this doesn't work you may want to do some research on epsom salt. But try the pea method first! Good luck!
Edit: Basically what a pea does, it helps them poop out all their food. If you get reccuring bloat issues then try epsom salt. Always feed 3-4 pellets a day. You can do 2 pellets in the morning, and 1-2 at night.