DH had way too many beers yesterday and was talking up a storm.  I kind of had things figured out about what transpired.

BM became unblocked because she was with SD's and sending him texts and he wasn't responding.  SD's called him at work and asked if BM was blocked because "they" were trying to send him something.  Because SD's were involved he unblocked her with SD walking him through how to do it, although I know that he knows how to do this.  
 

I blocked her again and I told him that she needs to stay blocked. SD's are really putting a guilt trip on him over this.

The SD's also told him that BM and her DH are constantly fighting and that BM told them she should have stayed with my DH and that she misses him.  They were married for 7 years, divorced for 5 when we met and DH and I have been married for 21 years.
DH told SD's that he would never go back with BM even if him and I were to split.

They asked him if he was happy in our marriage.  He told them yes.

Just out of curiosity I asked him what could I possibly do to repair the relationship with SD's and he said nothing.  They feel that if they showed anything in the way of caring, kindness, etc. to me that they would be going against their Mother.

He said that he reminded them of all that I had done for them over the years but he agreed that none of that matters to them.  He said that they did notice that I no longer buy cards or gifts and that they will remind him (of course they will). I did enter all of the dates on his phone calendar last year as well as entering the addresses in his contacts.

He was feeling sorry for himself because they were badgering him about joining them for family vacations with BM, her DH and their extended families.  He told them that wasn't going to happen but I have a feeling he probably said that I would never go for that.  I told him to plan his own vacation with them that didn't include BM.  He said that he couldn't afford to do that because he doesn't have the kind of money that BM' and her DH have.  DH has always felt that he must pay for everything when with SD's and their families. 
Nothing will ever change,  BM will always be lurking and yearning to have DH return to her ( they tried getting back together before I met him).  Skids continue to manipulate circumstances in an effort to get DH and BM together in hopes of a reconciliation.

21 years of this is exhausting.

I told DH that one more misstep from BM and I will be having a conversation with her DH as I am sure that he is clueless.  I told DH that I didn't do it before because of SD's but since there is no chance whatsoever of mending those fences that doesn't matter.  
 

I told DH that none of this is normal behavior and that she needs help.  He says that he knows but that she refuses to do that.

That's all I got for now.  Steplife isn't for the weak and in my case nothing changed or improved once the skids became adults.