Hags in Baldur's Gate 3 are not to be underestimated. If you ran into Auntie Ethel in Act 1, you'll know just how difficult they are to beat. Defeating a hag is a matter of besting their trickery rather than brute force, so it's no surprise you will find survivors of hag encounters seeking refuge in Act 3.
Baldur's Gate 3: How To Help The Hag Survivors
Act 3 of Baldur's Gate 3 sees you encounter other Hag survivors, along with Mayrina from earlier in the game — and an old nemesis.