Leaves yellowing and curling

This has probably been answered a million times, sorry! Tried to find photos from other entries to match against mine but could honestly not tell...

Growth has stalled for both plants, particularly the birthday cake strain. Purple kush is doing okay, but i worry i will kill both if i dont do the research. Both are in soil that I got from a seed starter kit and we have an LED grow light that we have on for about 12 hours a day. They're also next to a window, so I don't know if there is a negative impact from having 2 different light sources? I don't have a super set water schedule for them, but I check their soil regularly and water whenever it feels dry/light. I've started using a highly diluted plant food and misting the soil with it, 1-2x a week. I'm probably doing it all wrong as we've already killed 3 seedlings but would love any advice for a VERY novice newbie! TIA!

Photos: birthday cake (small, yellow leaves), purple kush (looks fine imo?), set up (ignore all the other plant bbs, showing in case our light is way too close or if grow light + window is a dumb idea! We have indirect sunlight during the day, so got the grow light), and plant food I've been using

With regard to your cannabis plants, they're stretching. That likely means they're not getting enough light. Cannabis loves direct sunlight all day long. It's fine to mix different colors of light, but be careful with changes. Give them at least 18 hours of light per day.

Your nutrients seem to have ammonium and a lot of urea. Soil enzymes break down urea to C02 and ammonium! Ammonium is acidifying and that could be an issue with cannabis, it may acidify the rootzone too much. Such acidification may be okay provided the potting mix has aglime (calcium carbonate) as a buffer. Your nutrients do not appear to have any calcium, its a needed element. Potting mix ingredients are important, what came with a seed starter pack doesn't tell us much.

How you water. Misting. Hmm. That may be okay. Generally you want the little plant to dry out the potting mix before the next watering, then once dry, a thorough watering.

Be patient with learning, with yourself, and your plants. Good luck.