In all honesty, if my in-law came to visit my children in my home and continued to ignore me even though s/he knew it upset me, I just might reach a point where I had enough, too.
Add to this the same in-law pulling aside my husband to bad mouth me in the name of love and proteching my children, and I would probably reach a point where the in-law's presence in my home and among my family was too toxic and would implement a time-out.
Like it or not, it behooves you to remember this is not your marriage, that is not your home and they are not your children.
If you visit with your grandchildren once a month, on average, why not be cordial to their mother as you build a strong bond with the children? It may take practice, but it just might be worth it.
Anyway, just my $.02. I wish all of you the very best.
Sounds like good advice.