If your water is cold, they MAY want to eat less... but 3 pellets 2x per day is a good rule. I feed 4 2x a day to my larger ones (in 78F water)
2.5 gallons is considered the minimum for bettas to live happily. I recommend Red Sea Nano HOB filters (silent!) and a Hydor mini heater (If you go the 2.5 gallon route.)
It might seem silly to go through the expense of upgrading them, but you will be SO surprised at the difference once they are REALLY healthy! The maintenance you should be doing on your tanks right now is 10000x more work than a heated, filtered tank (as long as it's cycled)
I have 6 bettas in separate tanks (2.5gx2, 5gx3, 10gx1) and it's no trouble at all to keep them healthy. I also have 5 ladies in a 20g sorority. They are a JOY to have... and SO different from when they were cold!
You will be able to find lots of help here if you have any questions about upgrades. If you choose not to upgrade, on 1 gallon tanks.. you should be doing large water changes EVERY DAY (especially important with fin rot going on). Clean water should brighten her up a bit. Medicine should not be necessary if the water is kept clean.