Regular poster with NC as details could be outing. Sorry for length, didn't want a drip feed.
I say SIL but it's my DH's brother's gf of 5-6 years - they don't live together, not married, no children.
DH's older brother is 42 and has always lived at home with their mum. Never had a full time or permanent job and spends all his time in his room, but no one seems to know doing what. Apparently a programmer but he's never worked as one and doesn't have a portfolio past the age of 25. I work in Tech and offered to get him a job at my company but he wasn't interested. He and DH don't get on as brother doesn't contribute to rent, bills, do any chores around the house - and when DH lived at home, he and younger brother had to cover his rent. His mum doesn't think he's on the spectrum and doesn't seem to display any obvious signs, is also physically healthy. He could of course be high functioning (don't want to armchair diagnose or cause offence, just to show there isn't anything stopping him working esp as we are in London with lots of jobs). My sense is he's just not incentivised to work as mum does everything for him, and dad and stepmum give him money when he needs it.
He's had a gf for 5-6 years though only mentioned her/introduced her 3 years in. She too lives with her parents a 60 min drive away (he doesn't drive so she travels to him mostly). It's an odd relationship as they don't see each other much, she only recently started staying over when she did visit, she does holidays alone as he doesn't like travel. But she's keen to get married as also 42 and keeps expressing her frustrations every time we see her that he isn't proposing.
She eventually bought a house in her suburb as got fed up of waiting and expects him to move in, contribute to the mortgage and learn to drive. We all know he will never do any of this (he's indicated as much) and is stringing her along though i'm not sure why she's still with him. It's been years of zero progress.
None of this concerned me as I only met her for the first time last year at a big family event and we aren't close to the brother, so didn't anticipate seeing her much. This is when she shared all their relationship issues - in front of him which was very awkward. However, I'm now pregnant and his mum is trying to create more of a family atmosphere by inviting DH and I over for meals regularly. The brother is always there of course and now so is the gf. And she takes out her frustrations with the relationship on me by haranguing me non-stop every time we are together. I can't open my mouth without her either contradicting, lecturing, patronising or arguing with me - on things that don't concern her at all e.g what my life was like in my home country (she's never lived there), my pregnancy, raising a child and mat leave (she has no kids), how my parents manage their finances when my dad passed (??!), my career (I'm 4 levels more sr than her in same career). She also practically yelled at me because i don't drive which really felt like she was yelling at her bf (we live in London with excellent public transport unlike her and won't move). I suspect a combination of being triggered by my pregnancy and also the bf's lack of commitment.
She only directs this at me and her bf of course says and does nothing, just leaves the room when it gets strained. DH and MIL are both quiet, non confrontational people which doesn't help so she does most of the talking. I'm a direct person and have no objection snapping back (and have tried) but also don't want to feed the drama as looks like she's spoiling for a fight with me. However, MIL still insists on having these meals and inviting other relatives as well and DH and I dread them. I also don't want her anywhere near my baby when he's here - which is the real issue as it would mean never going to MIL's house and inviting her to ours instead. Which would upset MIL as she likes hosting and it isn't as easy for her to travel as it is us.
I suggested to DH he have an honest convo with his mum about why we don't enjoy these gatherings and may decline invites, but he is worried that it's her house and brother lives there so not inviting the gf or intervening puts her in a difficult position. To me this is a result of the brother letting his relationship drama spill into our lives and he should be managing it - but MIL doesn't like challenging him. Does anyone have a way to deal with this without it causing a rift?