It's magnesium deficiency alright.
Your plants aren't in generous sized pots, and so, if it rains a lot, or if you water as thoroughly as you should, this WILL leech out minerals and nutrients.
Although the deficiency that shows is mg, I'd bet that the problem is more widespread, in terms of nutrients.
Give immediately a soil drench of 1 HANDFUL of Epsom salts per gallon of water, followed at the next 3 waterings, by seaweed extract (which is an excellent, fast-working, re-mineraliser) diluted as per instruction.
a pinch of Dolomite lime (magnesian calcium carbonate) per pot would also help.
Loss of nutrients is, after over-watering, the most common problem with plants, especially fruit plants, grown in pots.
I notice, Ferice, that you live by the sea (if a name like Port St. Lucie is a guide); is there any way you could collect your own seaweed and make your own extract?
The really good stuff is quite expensive, but extremely easy to make.
I collect my own, soak it in water for 3-4 months, and use it. Seaweed picks up all the minerals in the sea, and I have read that it contains over 60 micro-nutrients!
It's good for slow-release potassium too.
Next time, when planting up your tomatoes, your chillies, sweet peppers, or any other fruit-type veg, you could add a handful of volcanic rockdust, which is also an excellent, slow-release remineraliser.
The top plant may have tobacco mosaic virus, and I'd isolate it from the rest just in case, but by far the two most common ways to infect plants are; with infected material in the soil (unlikely because you're a new grower using pots), or infecting the plants by handling them after handling infected tobacco.
So if you don't use tobacco, TMV is possible but unlikely.
I'm not seeing a whole lot wrong with your plants otherwise.
