OP, this is still in my mind, because your situation hits close to home.
I am really not even able to process how your husband (your BIL, thru your husband) is badgering you, online, AT WORK.... and you just 'gave in'.
OP, this is really much much deeper than any of us have realized.
This isn't about little petty crap like taking all the food out of the fridge.
If I were being badgered, online, AT WORK, and called a "%$$%$ &%@$&&".
That, seriously, would have been the very very end of it.
I would have either refused to respond at all, until I could speak face to face..
Or, my response would have been.
"I am sorry 'John'... I am AT WORK... You just called me "%$$%$ &%@$&&".
I will not be discussing any of this any more, until I see you face to face, and we can have a reasonable discussion"
Or, more preferably, "....face to face, in the office of a good marriage counselor".
It is hard to think that you have now become complicit in this whole thing.
You are allowing this to go on.
You have been participating in the whole 'engagement' and 'enablement'.
In fact, for me, the minute that I saw that the BIL's comments were asking your husband to speak with you, that would have told me that my husband had actually told BIL that 'I' was the one who 'wouldn't let him...' Throwing you under the bus. I would have told my husband that this was not acceptable, and requested some counseling, right there.
And, every dime of money says that when they return, BIL whines and manipulates, and 'can't go back his mother's'. EVERY DIME.
Again, OP, I am very very sorry.
I am sending hugs!!!