Yellowing and dropping those leaves at the bottom are normal. The plant doesn't need them anymore, so has shut off its lifeline to them. The spotting and styreaking isn't widespread, so I tend to think it is a combination of things, including outside damage of some sort, hat stress, lensing of water or dew. Nute deficiencies will show up in specific patterns, in specific areas of the plants.
If you're feeding and watering them all the same way, and it's not just one strain being affected, and most of the others look healthy, then there is SOMETHING external happening. By now most of the larvae have become flies, moths, or whatever. Just trying to remember what insects I had to deal with, when I had a vegetable garden in Ester.
I did have occasional cabbage worms and some that ate turnips, and definitely something that chewed holes in the leaves. But that was all outdoors, not in a nice greenhouse like yours.