Are these stretching? What should I do for the 2x top that barely sprouted?

Yes, a little stretched due to not enough light intensity, but nothing major. 50% intensity at 24 inches will be fine. The other two will catch up soon enough, nothing to be worried over. If you are OCD and NEED them to be level, just sit the top two pots on a plank of wood or something similar, to raise them closer to the light. Seeing as how you will need to transplant these seedlings soon, those pots are way too small for good development, planting the taller ones deeper, so that the soil goes half way up the stems, should even out the differing heights of your seedlings. An inch or two in difference of height as in relation to the light will not make any difference to your seedlings' growth, health or anything at all really. Black plastic pots about 4 inches across and 5 inches deep are ideal for your seedlings first 3 weeks of growth and root development (very important!) and if using decent soil, will not require any extra feeding. If looked after and cleaned between cycles, the black plastic pots will last many years and can be used over and over, making them very economical in the long run. Little cups dry out too quickly, have much too small an area for root development and run out of nutrients very quickly, handicapping your baby seedlings growth rather soon. Just remember, a plants roots will be 2-3 times as long as the plant is tall, meaning your seedlings roots are already at the bottom of those small cups. For some pictures of a 3 week old seedlings root system, go to my diary "cannabis conundrums" and in week 7 you will find them, as well as many other pictures of weird and wonderful things cannabis plants are capable of doing. These pictures of the exposed root system of the 3 week old seedling may give you an idea as to why deep pots are so vital for a seedlings development. It always amuses me that people want to grow the biggest and healthiest plants they can, then start their seeds in tiny thimbles with barely enough room for a weeks growth! Hope this elps, Organoman.