@GoAdvertFree I don’t think you’re being unreasonable at all -your SIL’s expectations are far outside what’s typical in a divorce, especially at this stage of life.
She hasn’t been a SAHM to small children for years. The youngest is 13. She went back to work after the separation, found a role that suited her, and then chose to resign. That’s not “burnout”, that’s opting out. Courts don’t reward someone for voluntarily giving up income.
A 70/30 split because the teens live with her is not how financial settlements work. Teenagers are not toddlers. They are in school all day, increasingly independent, and one is already at university. Child arrangements don’t justify her claiming the majority of the marital assets.
Her wanting a 4‑bed house in an expensive area, a lump sum for savings, her mortgage paid by your brother, and to remain unemployed …is simply not realistic. It’s not how divorce finances work in the UK. Judges expect both parties to maximise their earning capacity, especially when children are older. She doesn’t get to resign and then demand to be financially maintained at the same lifestyle level.
Your brother buying himself a flat and renovating it doesn’t mean he’s “hiding money”. It means he’s been living separately for years and has provided a stable base for the children when they’re with him. That’s normal.
If anything, he’s been extremely accommodating, he’s continued supporting her, paid off some of her personal debt, and allowed her to remain in the marital home long after the relationship ended.
Her demands sound less like legal reality and more like panic, entitlement, or magical thinking now that she’s dating someone new and imagining a fresh start funded by your brother.
I could get my head around the fact she wants a 70/30 split because of the kids but why she thinks he would then pay the mortgage for her new home is beyond me. And will she get a mortgage without an income - I'm assuming he won't be able to get it in his name as he will be paying his own mortgage and won't have the credit available. He needs to pay maintenance for the kids but from the sounds of it he is a good man trying to do his best,
Financial mediation is fine, it’s standard, but it won’t produce the outcome she’s imagining.
You’re right: most people in her situation would be increasing their hours, not resigning and expecting to be kept.
I agree with your thinking, but keep out of it, she will find out the hard way when it comes to the financial settlement.