I'm not sure if your problem is about your mil or your husband wanting to communicate with his Mum through you.
I can tell you many, many mothers-in-law become jealous of the close relationship their son has with his partner and begin to feel left out.
Motherrs have a long history of all their child's attention being on them.
Their sons (and daughters) have relied on Mum to provide all their needs, solve their problems and often smooth paths and be the barriers between them and trouble.
It doesn't come easy to let go. But let go they must if they are to maintain any sort of positive relationship with their adult children.
Holding on, resenting the daughter-in-law (or sil) and trying to interfere does, as you know, endless harm and can ruin any good relationship.
But how do you persuade a jealous Mum-in-law that you are not a rival, that she doesn't need to fear you, or that you'll 'take him away', that the more she claws into him and criticises, the more he'll pull back?
If you have both told her, kindly and sympathetically that you understand that it's a kind of grief but that she hasn't actually lost him (but will if she doesn't stop) then she's been given her chance. If you haven't done this, consider doing so.
I have 2 sons and the relationships between me and the boys could not be more different.
No.1 son will not speak to me because years ago his long-term girlfriend was jealous of our close relationship. He cut contact with me and his brother because that was easier than battling with her rampant jealousies.
No.2 son is entirely different.
Given a similar scenario, would have told the girlfriend he was keeping contact with me and she could like it or lump it.
He contacts me several times a week by sending links to TED talks or videos he thinks will be of interest (currently it's about Artificial Intelligence and 3D printing of body parts!), rings regularly for long chats, usually as he's driving to and from work as it ensures privacy, and often comes here for a whole day.
He hugs me the moment he arrives and before he leaves; he never eats a meal without some remark of appreciation and always washes up afterwards (all this happens at home too, it's how he is).
He lives across the other side of the city but would drop everything if I needed him but even when I was rushed to hospital I didn't tell him, knowing this would happen and there was nothing he could do.
Once it was all sorted out, I phoned him .
I could not have a more thoughtful and interesting son. He's highly intelligent, interested in a myriad things, has a responsible job at the university and I've never met anyone who doesn't like him.
Yummysushi is such a cute name - we have a little shop in a nearby town with that name, makes the best sushi ever.
www.zomato.com/auckland/yummy-sushi-glen-eden