BudMother I feel for you as early on I killed a few of my plants with overwatering/nuting (at the time I was using liquid MG too) but I never saw any seepage from leaves like you're describing. Generally when it is an over-nute problem people advise flushing but obviously this is only going to make the overwatering problem worse, however allowing them to dry out if they have been overfed might make that problem worse. I am pretty new to growing myself so if anyone more experienced offers other advice, I'd definitely listen to their advice first but you could try this:
As you have 12 plants and they are all in a bad way, you could divide them into three groups and try different things on each group. That way you might be able to save at least one group and if you noticed an improvement in any group you could try doing the same things to the others.
Group 1: Do nothing and hope for the best.
Group 2: Flush plants to try and remove fertilizer then repot into dryer soil, trying to remove as much of the old wet soil as possible. It would probably be a good idea to get the flushing water roughly the same temperature as the current soil to avoid shocking the roots further with cold water. Try to keep new soil as loosely packed as possible. If stem is really weak you can bury it a little deeper as long as no leaves are buried.
Group 3: Try to speed up the drying of the soil to see if this helps or worsens the problem. Possible ways to do this: Squeeze pots firmly at sides to try and loosen soil and stop it compacting. Hopefully some cracks will form in wet soil assisting with aeration. If not, consider making some holes in soil with chopstick/pencil etc (this could be risky for roots). Place pot on some kind of elevated surface that will allow air to circulate underneath as well - a cake cooling rack is excellent for this or if you can spare a shelf from fridge/oven, elevate it on either side so it makes a shelf. Space pots out as much as possible to increase general airflow around them and run a fan in the area (if stems are really weak, stake them first and avoid having fan blow directly at them initially). If pots are flexible enough, carefully make some additional holes or slits in the side with a craft knife or similar or carefully insert blunt knife/spoon handle etc between the side of the pot and soil and then try to get something absorbent into this space. Perlite is good, kitty litter is ok if it is the plain variety (usually the most budget type) that hasn't been treated with any kind of sanitizer or other chemicals. Water retaining crystals are good as they soak up water really quickly but they have to be used sparingly as they expand heaps. You could also try paper towel and use the knife/spoon to press it against the side and top of soil to encourage absorbtion. Keep changing sheets before it gets too soggy and breaks up. Dry wakame seaweed also works well with this method - it starts off looking like tagliatelli so you can get it down the side of the pot quite easily but ends up about ten times the size and is very rubbery so you can pull it out of pot when it has absorbed a lot of water.
You could also consider on all/any group, misting the leaves with some clean water and drying immediately with tissue to remove any residue of the seepage that you were talking about.
Before you start, it might be worth sacrificing the worst looking plant and having a good look at its roots to assess the damage. Posting some pics of this might help others diagnose problem also. This will give you a better idea of the root placement in the other pots if you're going to do things like poke hole in soil and will also give you an idea of what areas of soil to target for removal when repotting. If you're as gentle possible with it you could even try replanting it when you've finished.
Might also be best to keep them inside for a day or two if you have a light or a well lit windowsill so you can keep their atmosphere constant and use a fan. Being in a bad way they would be quite susceptible to temp changes/pests/fungus etc outside. If they have to go outside make sure you put them somewhere sheltered so they are shielded from any sudden downpours or strong winds.
Hope you manage to save a few of them. Best of luck to you.