if bringing down quilts, I would only ever bring a breathable bivysack.
If considering bothy bags, have a close look at the actual sizes, they are even more fanciful than tent sizes.
i have the RAB superlight “4person” bothy, and it is tight with my familty(none of whom are very large, 2, adults, a 9 and 12 year old).
Since it is only 5’ long(I think) it would not be possible for two adults to lie down inside it, and of course, it’s not breathable.
i bring it on day trips, for the value of a sheltered rest area, especially with kids, and in case of emergency, it can be a hang out.
If I truly am concerned about a forced night sleeping out, I bring a waterproof breathable bivy, usually just SOL, because my others are older and heavier than a mid style tent.
i really wish someone like Zpacks would make a lightweight bothy bag with super light breathable fabric and cubes, and in a bit longer length, so it could be used for both breaks and emergency nights out.