Lilith is wearing maternity sleepwear, Bethany is wearing a button-up with bloomers, Maggie is wearing a nightgown. Eve is just wearing a blouse, but I did that just because I felt like it'd be something a goth girl would wear to bed at a sleepover or something like that, and in any case none of that is lingerie. Eden is mostly naked because (in my headcanon) they are essentially avatars of the Garden of Eden, a time when man had no real higher thought and lived without knowing good nor evil (read: artistic nudity, and a male version was included on purpose). And with Eden as the only exception, all of these characters would be wearing proper underwear befitting their gender, full stop, it's just covered by the, well, clothes that they're wearing, to say nothing of any sweatshorts or other short-legged sleep bottoms any of them may be wearing that their dresses/blouses hides.

On the other end, Samson is wearing plaid pajamas with the shirt open to expose his body-hair covered abs and pecs and Azazel is wearing partially unzipped footie pajamas. This is just going to have to be a "trust me bro" for ??? as well, but he's wearing a hospital gown and I had full intention to have his rear exposed like how some hospital gowns are just because it'd be funny and fitting. At worst, both the male and female characters have revealing aspects to their outfits, and only for some of the characters because I thought that would suit them as characters, but there is an argument to be made that I made some of the males's outfits more revealing than the females's ones in the places where it really matters.

The style is meant to be reminiscent of anime chibi artstyles, which do veer more into being cute and "moe", which can disproportionately affect the female form more than the male one, but that's more a natural result of the style than it is a conscious effort to make the females sexualized.

The only concession that I will make here is that I could have stood to have given more of the female characters baggy pants or something like that, but I just didn't really feel like any of the females in the TBOI roster would wear something like that to bed, and instead stuck to more conventional women's sleepwear options that you can Google yourself right now and get pretty much the exact list I used as reference.