I'm guessing you've tried to convince your mum that no, he's not a good person and not worth the stupidity and abuse he puts you and her through?
Err, IMO, it's maladaptive behavior (As in 'interactions that may not really be healthy but 'it works to get results') which continues as a process affecting other people. Which could detail why Caroline's background may be like it is.
That said, OTHER THAN DISCUSSING the familial ties of Caroline's background--I do believe support towards her is the first priority anyone here should give other than that. Because firstly: Nobody knows her background other than her--she knows it best, and she can detail it in a way for others to know better, but that isn't her priority here since we cannot solve this for her. We can help by redirecting her to places where she can get help or help her out with what she's in control with, but discussing her familial life may not really be helpful at all. It's the pseudo-cyclic nature of behavior that comes off as abusive, it stems from maladaptive behavior, and reinforced by the lack of other ways in interaction, to be extremely blunt.
I do believe the Catholic Church has annulments. Also known as 'this marriage never happened in the first place'. (By 'believe' I mean 'know', by the way, but, well, sometimes turns of phrase just work their way in and etc..)
There's also the lack of divorce in countries which strictly practice that. :O ...With my country as one example.
I will be okay. Thank you for worrying, though
We're all just concerned for you here.
Please do take care there, and keep in contact with your friends and other folks--to also help your parents and otherwise in the future too.