It's a continual victim mentality that the world is against them and causing them harm.  The same disordered thinking also leads to thinking the worst people in the world will always be there for them no matter what.

Does your wife's family confront her about this behavior at all?  It sounds like they're enablers. 

Have they expressed any sympathy or concerns to you?  I've read accounts of both times of families here: those that side with and enable the pwBPD, and those that actually warn the non-disordered partner away from their son or daughter, or try to at least. 

It was interesting to see the dynamic when I met BPDxw's parents & extended family.  They didn't speak English, so I had to judge from body language and tone, but it seemed like other than her mom, who spoiled her a lot and I surmise contributed to her laziness and sense of entitlement, NONE of them tolerated BPDxw's tantrums or gave in to her.  As I understand it, during her childhood, BPDxw's mom alternated between completely abandoning her to chase after her dad, but then spoiling her when they were around to compensate for the lack of parenting.  I've read that this abandonment/spoiling combination is really the absolute worst when it comes to bad parenting and child rearing (that's consistent with what I experienced). 

Anyways, other than her mom, no one in her family seemed to tolerate her behavior, or give in to it.  I noticed when we were there, the only people that got any grief from BPDxw were her mom and I, i.e. the two people who tolerated/enabled(?) her emotional B.S.  And of course, she eventually left her country to come to the U.S., so I feel like that's the M.O. of the pwBPD: churn through relationships until you can find situations you can control and monopolize the attention; if not, you blow things up and move on - including leaving your own country - until you find better enablers/doormats. 

As far as concerns about a potential divorce fight & that unpleasantness, I'm sure you've probably read some threads here around divorce advice, but absolutely DO NOT let preparations for it linger until the last minute. 

If the pwBPD starts to sense their partner is checking out, they tend to escalate things - i.e. the "extinction burst" - to try to get them back in line.  If you're starting to see divorce as a possibility, then it's better to have your ducks-in-a-row and ready to go if/when police get called or there's some other sort of blow up.  Have an attorney picked out, ideally one you've met with and who understands your situation.  Have some emergency funds stashed away, and have a plan for where you'd go - with or without your kids as may be necessary - if you have to leave the house for a spell and file for divorce. 

And of course, keep all this to yourself; do not leave any evidence of your preparations lying around.