Three of your fishes died the other ones look like they were sprinkled with salt and also their fins rotted away and will their fins and health restore back to normal also is it infecting?

I'm assuming you have a tank, heater, thermometer, filter etc because they are the basic requirements for keeping fish. Your fish will all die if you don't look after their water conditions properly. I would do a heap of water changes and to kill the white spot (Ick) I'd raise their temperature to around 85F-87F for a few weeks.