So, you don't let seedlings wilt. Like just never. If you're having problems with watering, just spray the surface. Literally spritz it with a water bottle. This is how I do it. I don't have any problems with overwatering, or damping off.
The calcium in coco coir was my recommend. Your plants all look like they're suffering the same. You cannot turn coco coir around that quickly with just egg shells and water. Eggshell needs time to break down. I recommended to you that you use vinegar to create calcium acetate. You said that was too complicated. I also said if that was too difficult, epsom salt would be a good second choice. You said you had a solution.
I reserve the right to be wrong, but these plants look exactly like what I've seen in the past with a coco coir substrate that didn't have a calcium pre-charge. This has 2 effects: 1) the media may retain salt water - calcium releases it, 2) No calcium means that N, Ca, and K are locked up in the media.
You ideally need to do the charging BEFORE you plant out. I'm not 100% certain that you can save them as seedlings, but to me, that's your best best.
At this point, I would HONESTLY just consider removing all of the media from the seedlings, and just putting them into your MG mix. I don't think they're ready for a mix with ferts yet, but I also don't think you have a great chance of success with what you have now.
A final option, would be to properly charge that seedling mix, and then remove the old mix, put the seedlings in the newly charged, and see what happens.
All of your plants are way too small to be clipping leaves. I think you may have really misunderstood that bit of advice. We don't trim leaves, until we actually have a surplus of "true" leaves. That is, when your leaves closest to the bottom are not your only set of "true" leaves, then it's a much safer bet. Truth be told, you never need to trim leaves, period. Certainly, you don't want to be robbing a plant that's already in bad shape, of any surface area that can aid in recovery.