Yup. There's no clear definition for either of these terms. It depends on who you ask on whether or not there can be overlap between bara and yaoi, or if something can be both bara and yaoi at the same time. I personally don't think there's overlap but I also don't think everything that focuses on a gay couple and isn't a yaoi is bara. Heartstopper isn't a yaoi or BL, but I wouldn't call it bara. I'd say it's just a gay-themed comic. And I'm not going to dismiss anyone who describes their work as both yaoi and bara although I would tell them that they should go with one or the other if they're friends of mine. Generally speaking, yaoi is for both women and gay men (with more focus on women) while bara is usually only for gay men and is more overtly sexual. For me, I feel like the way people use the word "bara" is quite broad that I can't really put a strict definition for it. And people do describe SFW material as bara (Is Minotaur Hotel suddenly not bara when you play the game on SFW mode?) so I don't consider being NSFW a requirement to be bara.
Well I didn't label it as TL;DR because I think a proper TL;DR would be quite long XD, but here's what I was talking about when I talked about putting in a "TL;DR"
"All in all, bara is a word that describes the sexualization of men that are muscular, beefy, and/or hairy for the benefit of gay men. It can tell many gay stories that the mainstream cannot tell due to not being afraid of showing the perspectives and tastes of gay men that aren't young and conventionally attractive. It is a wonderful thing that has plenty of potential, but it can also be used poorly. We should strive to develop our community so we can reach greater lengths with bara."