WTBH,
I'd block all contacts from these in-laws.
Another thing I learned about 10 years ago when I was getting mean, nasty emails from a niece. (Passive-aggressives do that; they say things in the email they wouldn't say to your face.) After a few nasty emails, I decided that from then on, anytime I'm reading an email from ANYBODY and it gets nasty---that's when I stop reading it. Or any other emails from that person.
Best to you--keep comin' back.