Hi Wolfy, poor babies, I hope they get to feeling better soon.
I'm going to throw some questions out here.
Kate has already asked, what are you feeding them, how much and how often?
I looked at your aquarium info, it lists a 5g, are the girls together?
You said your water is fine, Are you testing your water? If so what are the readings for ammonia, nitrites, and nitrates?
It also says you don't know about the nitrogen cycle, is the tank cycled?
Here's a good article to read:
http://www.fishlore.com/NitrogenCycle.htm
Do you have a heater? What's the temp. of their water?
This information might help others help you figure out why your girls keep getting bloated.
Good luck to you and Lady Lune, and Lady Sidereal.