Looks like you have a couple of issues at the same time. Slight overwatering, slight nute def.- most likely P. Heat may also be an issue. A stray mite or two.
First rule out overfert/lockout, it can mimmick underfeeding, flush thoroughly.
Start nutes again at the next watering at LOW PPM, ramp up nutes as needed, might take a day or a week to get to a proper PPM. Watch em closely!
Both of ya'lls plants look to be nowhere near big enough to need transplanting. They can get up to 12in. in those beercups with no trouble. C5 is spot on with final pot sizes, but moving up too fast can encourage roots to head for the edge of the pot and start to circle the pot repeatedly instead of filling the interior soil, not good.
Just my 2cent, I'm no expert by any stretch.
Read Uncle Ben's sticky at the top of this forum. It's the first place I go any time I have a problem of any kind.
Hope this helps,
Fred