Ich is a parasite so fish can not become immune. It is in the tank now so there is no point isolating the infected unless if makes you feel better.
Increase temp slowly to 86-88F
Increase water changes and gravel vacs
Leave temp up for at least one week after last spot is seen
Slowly decrease temp to normal
You can add a little salt if you like. It can help avoid infection in the sites where the ich leaves the body of the fish. Plenty of clean water helps a avoid this also.
This is the way I did it, and I had MILD Ich. This is the best way, no salt though Valuable Cories.