As I suspected, the white(ish) at the edge of the fins is normal not fungus The tail looks as if it were bitten so I would suspect the Silver Dollars for doing that vs the bichir. For the time being, if you can separate the tank so that the Oscar is on one side and the Dollars and bichir are on the other side and keep the water clean, those wounds should heal on their own. If you notice any redness or fuzzyness at the wound sites, the fish would need to go into a hospital tank and be treated with whichever antibiotic is appropriate for your water conditions. If using a divider is not possible, you'd need to rehome either the Dollars or the Oscar as they can't stay together.
Possible reasons for the Dollars chewing on the Oscar include improper diet or not enough food/ feedings. Silver Dollars will do better with small feedings throughout the day vs one larger feeding once or twice a day. The Oscar, depending on what you are feeding it, may only need a feeding once a day if you are feeding live foods or if you house say, smaller food fish for him to eat at his desire. If you are feeding dried foods, they are best fed in small amounts multiple times during the day as well so the fish does not get overfed or constipated.
Hope this helps.