Brown points and yellowing

5Lt pot? Thats half the prob. Small pots dont hold a lot of nutes, so you need to feed more often, so these plants are hungry and need feeding. Thats the likely cause of the yellowing. So what ever nutes your using, mix some up and feed them asap!! And brown at the top is DEF not good, is it mold brown or is it light burn brown? The light burn brown starts off yellow or even white before it goes brown, while bud rot/mold is just brown from day 1. If your humidity is not around the 45%-55% range, fix it soon, anything higher than 55% in flower is asking for bud rot. Get more air flow and get your fan or fans blowing harder.