Here are the areas I'm worried about a little bit closer

This one--the little bits of withered looking plant, the splotchy areas, the wrinkled under leaves. What happened to the plant that made it do this and what can I do to correct it? Is the underside normal, or is it a sign of over/under watering?





This one--The white 'holes' with the brown ring, the fact that it's losing leaves, and the amount of plants packed into a single pot. I know they do good in tight spaces, how tight is too tight? Should I separate these plants? Again, what's causing the little yucky parts turning brown and losing leaves?




They don't look BAD, but I don't want them to get worse. Should I just continue like normal and see if they get better with regular care(maybe recently recovering from under/over watering from the shop?), should I intervene and repot them? Should they get more or less sunlight? Are these just normal plant things or signs of bad care or an infection/parasite? Those are my basic questions. I'm new to plants in general, and I don't want to mess up here!