Betta is Flashing and Twitching

[DoctorWhoLuver]

So it all started with Avalon who had stringy poo, so I assumed it was internal parasites. However, she passed away before I could get the right meds... :'( The Petco and Petsmart near me did not have meds for internal parasites!!!
Then, Raxacoricafallapatorious started getting all clamped up and also had white, stringy poo. However, she also developed a twitch and is flashing around, so I think it's some sort of parasite... I'm treating her with Aquarium Salt because that and malachite green are all I have. I'm scared to treat her with malachite green since it's toxic and I'm not sure if she even has external parasites. It's nothing I can see. The blood vessels around her head also seem redder.
Now Martha is acting lethargic and clamped up... I'm really at a loss and I don't know what's wrong.
I don't have a water testing kit.
Tanks is at 82 degrees
They were in a 20 gallon sorority of 8 girls, but are now floating in hospital tanks.
No medication, except for AQ salt.
All my other fish seem fine... but I don't want to jinx it... the last time I had a disease outbreak, it turned out to be columnaris...
Please help.

[DoctorWhoLuver]

Could it be gill flukes or body flukes? Or are those visible?

[DoctorWhoLuver]

Update: she doesn't move except for the occasional flash or twitch.

[DoctorWhoLuver]

I noticed that Martha lost a few scales and seems to be developing dropsy... The good news is raxacorica is eating again, but she's still very clamped up.

[Tikibirds]

gill flukes need a magnifying glass to see.

I had a fish with the twitch and treated him with furan 2 - although I am not entirly sure what his problem was.