I don't think you are totally fucked, especially with your monster outdoor plant. Have you tried flushing them? If the leaves still look like they did the pic it is worth trying to recover. One of the other posters mentioned 15 gallons, which is 3x your medium. Its worth a shot. If the biggest plant survives you have two options, you can LST it down, and let it flower out, or turn it back to 24 hours of light, turn it into a monther, take a bunch of clones and then flower those. You'll be a few weeks behind but not dead in the water.
You can still recover.
My suggestion is for your next grow, rather than trying to add nutes and worry about burn, just follow a soil recipe that requires only water. I use moonshine mix, Subcool has his super soil, there is LC's soil mix #1 and #2 I think, also blaeoneup's soild mix. That makes it super easy for new growers.