I will echo what Flickety said.
One of my DDs has had this problem, added to which her FIL has also been absolutely vile to her. Jealousy is at the root of it.
It has taken many years and SIL actually overhearing them being nasty to DD before he stuck up for her and things are slightly better now.
We stayed out of it, just providing support and a sympathetic ear for DD when things became very upsetting (which was often). It is very difficult to stay out of it when you witness it yourself but probably best in the long-term.
To think that London, or anywhere else for that matter, does not belong to any one demographic