I though drama were behind us. 

Today MIL called DH. DH answered cause he though it was about his grand mother who has cancer. 
MIL was furious, out of nowhere. 
 

She claimed that DH didn't wish her merry christmas. He replied by saying that since she doesn't treat DS like SS, he doesn't want her to be part of our family. 

MIL started arguing about SS braces fees. That DH didn't payed for anything, so she has to help BM to pay the bill. 
The fact is that few months ago, BM asked DH to pay half of the bill (many hundred €€€) for SS braces. DH has a good (and expansive) health insurance, but BM never sent any document in time so DH insurance was not covering it. He said to BM that since she didn't send any document as he asked multiple times, it was her problem. He said he will pay next year if she does the job. 
 

MIL put this story on the table again, arguing that she was not capable to pay for SS braces AND to offer gift to DS. That SS braces were necessary, instead of DS gifting. That DH was not doing his job as a father of, so she must compensate and she has not time to play DH role to SS AND a grand mother role to BS. That of BS has a heart, he would understand when he will be on age to. (Bty, good luck with that MIL). 
DH has no idea MIL was paying for SS braces, but that not the point right ? 
 

And the, horrible things about me : that my only point was to make DH cut ties with his family and his son, that my family was rich and put no effort on SS, that i was making differences between the boys... 

From this talk, DH is exhausted, so do I. 
I 100% know that all these stories are not SS fault, that he has negative influence from this side, but i can't help myself having resentment for him. 

Thanks again MIL !