Are these body proportions realistic (2)?

yeah the proportions on most of everything are fine just work on the head a little. make the hair somewhat thicker so that it looks like it would adhere to a natural head shape and not just lay there on nothing. like i said though its otherwise perfectly fine.

The muscles seem way too defined in both. Unless you're trying to make them look like body builders, it looks weird haha. And the waist on the second is way too thin.

The proportions are fine, although you might want to try making the head a little fuller and less skinny looking. It's good otherwise.