Have any more fish died in the last 24 hours. If not, then maybe wait a few more days and see how they go. You can post some more pics of the remaining fish and I can see if they look normal.
Normally if they have a disease it will need to be treated otherwise they will die. If they don't have a disease they don't need to be treated. However, the fact fish are dying and they are spinning in the water, and they have a weird colour on their bodies when dead, is an indication they have a disease.
If you don't want to treat them then just do big water changes each day and hope for the best.
You can treat the main tank or move all the fish into a quarantine tank. However, since they are in a tank, you may as well treat the display tank where they currently are because it will be less stressful for them because you won't have to catch them to move them.
If you get a medication suitable for scaleless fish (catfish, loaches, eels) then they should be fine. If you can't find a medication that is safe for scaleless fish, then use a normal medication at half strength.
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If you have lots of plants in the tank then gravel clean around the plants.
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If the fish have a disease, they would have had it at the shop before they were put in the bag.