ctvu ... don't buy a plant ... you will be mucking around with it and the driftwood too much ... will give additonal stress.
Keep temp const, above 32 degrees ... keep the tank dark and try to avoid traffic in front of it.
Regular water changes, if discus too stressed from 50%, then drop to 25% daily. Your good bateria will grow. If ammonia problem ... reduce feeding ... but still feed if they are eating, but not as much.
Even dirty sponge filter might have heaps of good bacteria on it , just rinse it in fish tank water ... pop it back in.
Keep the spirit ! Its heartbreaking I know seeing sick fish, but my attitude is, I am not going to give up until they give up ... it our duty to provide the best conditions for them to recover ... we don't give up on them !!
Sometimes they just have a cold.