Keep the lines of communication open no matter how hurt you may feel at the moment, your son may well need you in the future.
If asked, explain that you had family problems when your DIL was pregnant and that you didn't mean to neglect the two of them, point out that
you are a daughter as well as a mother and that you owed your father care and consideration too.
I can't really cast any light on why the situation has occurred but I have seen similar situations before, usually down to jealousy or insecurity on behalf
of the guilty in law. I didn't like my ex's alcoholic mates coming to the house because I didn't want my children near them, this didn't go down well with his mates naturally.
You could ask if there is anything that worries your DIL about the family? Sorry if this sounds rude, I don't mean to be offensive, I'm just trying to think of anything that could have
created the situation? What seems normal to us may be strange to your DIL.
Did you reply by telling her that under UK law there is no such thing as a necessary heir, which means that you can leave absolutely everything you possess to the dogs home
LOL My mum used to do this when my brother and I were being daft teenagers, never worked because we never assumed we'd inherit anything anyway, we just got her a form from the local cat place ( we both like cats) so she could do it if she wished!!!! Mum was horrified that we could contemplate leaving money to any animal!!!! Both of us would still be very happy if she left her money to a charity!!! better still, blow it on wild living as she's worked hard all her life and deserves lots of fun!!!
pmddx
I hope your situation resolves it'self , just be there for your son no matter what because he will need you one day.