Need some advive...

Is it possible to save these? Setup led, soil, some nutes unknown ph.

3-4 weeks left to go.

You'll be able harvest, but what damage is done is done. So...what did you do to make this happen? Mark it down as a learning experience.

It looks like there starving. Plants will yellow when there near the end of their cycle. You could feed them but then again you might burn them. I would just grow them out.
That one plant looks bad with all the spotting and thats a magnesium deficiency but I think this far into the grow there's not much else you can do but grow them out. Try some cal/mag. Deficiencies usually are caused by incorrect PH causing lockout. I see you don't know your ph, you should focus on that.
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I agree with popcorn, use cal/mag and get a PH pen or worst case litmus paper. PH is more important than a lot of people think.

feed them. look calcium hungry. I would feed them my veg and flowering nutrients mix them the rec dos . do not over do it. if you have no idea . in that late of a flower I like a
5/55/30 around that solution. will be ok. and don't panic you will be ok . trust me I have seen a lot worse in peoples gardens . just get them food for a week or so until your ready to flush if you decide to .