Sudden Case of Ick - Blood Parrot Cichlids

In my household, we have four parrot cichlids in a 26 gallon with two plecos. I know this setup isn't ideal, my dad is the main caretaker and he doesn't do much research. :/ We've had them for about 3-5 years now, I think.

About 20 minutes ago, I noticed something wasn't right. They were all lethargic, clamped fins, white dots on their bodies, and darting against decor. They still seem to have their appetite though. I'm not sure exactly how long they've had ick, I'm thinking it started yesterday. I was gone most of the day yesterday and I haven't gotten a chance to look at them in the last couple days because of school.

I also noticed one pleco is now dead, I'm not sure how long he's been dead, but the last time I checked (about 3-4 days ago) and he was still alive. The four parrots and the one pleco all seem to have ick. Can ick be immediately fatal?

So, I read the disease section about how to treat ick for bettas but I'm not exactly sure how to do it for parrots cichlids. I haven't added any AQ salt yet, and I don't think we'll be able to do daily 100% water changes because it's a cycled 26 gallon. Help please?

/edit
My dad is doing a 50% water change right now, can I use the same siphon he's using to clean my betta tanks? I don't want them to get infected too.