looks like they are coming along pretty good the soil may be a little dry and I dont think its a nute deficiency because they were yellow when the plant was way less mature. Try giving them a bit more water and make sure the light is not to far away. The bottom leaves will yellow and die but usually after its a little more mature. Now that they are old enough try using diluted water soluble nutrients and maybe even get some ph testing strips to see the run off PH level