This is pure magic on film. Take 8 min for yourself.
I have had, lost, regained more material wealth than most will even dare to dream of. Dad died, grandparents and uncles who raised me died, dog died.
Me and lady pain know each other well
Todd always got me through it
Not enough nitrogen 1st week of flower. Yellowing and leaves falling off from bottom says this. Nitrogen is mobile.
You need to defoliate your lowers to focus energy to bud production.
Use some P and K right now, nothing crazy but they need some. Your soil looks wrong texture and humidity. Try to aim for more smaller waterings instead of fewer larger ones.
Increase humidity and look up VPD
Increase light intensity. Your hand should barely or not feel it at all, 2-4 inches over the plant. They look slightly stretched to me.
Increase humidity. Look into what VPD is. Your plants are unable to "breathe" right now.
Be careful with solo cups and over watering/causing root rot. Your dirt looks a little dry but overwatering can kill faster. Make sure there is multiple drainage holes in cups.
Turn the fan lower 1 setting, or aim it up higher, so they are getting slightly less constant air at first. When they are small and you are using the fan so much, you are blowing their air/humidity away before they can soak it up.