TL/DR for this - BM is histrionic, emotionally immature, exhibits black and white thinking, engages in risky behavior, idealizes and then devalues people, and is obsessed with thinking that people hate her. SS is taking on many of those traits. 

BM followed the classic idealization / devaluation of DH. When they met she treated him like he wa the most wonderful person in the world, then a few years into the relationship, she, according to DH, decided he was "garbage". When they got divorced, she had already snagged another man, now her "husband" (they are not legally married and I don't know why), whom she totally idealized. After this man got into a tussle with one SS, in which the adult got mad and pushed the 8 year old, BM insisted to DH that her "husband" was a "beautiful, beautiful man" and "more of a father to our children than you'll ever be." Meanwhile, three years after their divorce - when I met DH - she was still calling DH daily for emotional validation or to take her emotional aggressions out on him. She's also had several friends who were her "best friends" until she had a falling out with them, at which point, she made it her mission to tell everyone lies about these people in order to discredit them. 

She also has problems with binge eating, gambling, excessive shopping, and prescription drug abuse. In 2011, she and DH brought in a combined income of close to $250,000, but they were still not paying bills. Looking at his credit history for that year, every bill was paid 30-60 days late, if they were paid at all. There was also at least one write-off for something she bought for her business (on an account in DH’s name) that she never paid for. She also engages in other risky behavior - she didn't pay her taxes and then didn't file them for several years, even though she works as a CPA. When DH approached the IRS for Innocent Spouse Relief, they wanted him to cooperate with them in tax evasion charges against her, because they suspected she was under-reporting her income (she was). She also worked in a partnership when they were married and the other partner ended the partnership because he thought BM was embezzling funds from the company (DH knew this because BM logged on to the other partner's computer and read emails he had sent to his wife). 

She also does a constant push / pull with DH. She oscillates between telling him he's the worst person ever and his children don't like being around him to being desperate for him to recognize that she's "changed" and tell her she is a wonderful person. She once texted him for three hours straight saying some variation on "why do you hate me?!" over and over and over again. She'll do things like this until she provokes a reaction. 

For their entire relationship, even before they were married (what DH was thinking in getting married, I will never know), she would verbally abuse him. She would also hit him, but he's a big guy, so she never physically injured him. After BM filed for divorce, they saw a counselor and the counselor told DH, "divorce would be good for you, because she's abusive." DH didn't believe the counselor because he didn't think men could be abused by women. In the time I've known him, she has told him several times that his children hate being around him, that it's traumatic for them to see him, that he's a deadbeat dad, that he's stupid, that his best isn't good enough...and on and on and on. 

She is also enmeshed with one SS. When she is mad at DH, this SS is mad at DH. When I first met DH, the kids would tell him that she would say to them, "why are you always defending your dad? why don't you defend me?!!" They were 8 years old at the time. Now she spends her time telling SS how much DH and I hate her, how we are trying to take SSs away from her, how this SS has a "bad" relationship with DH. SS doesn't know where his feelings end and his mother's feelings begin. She is constantly sending DH messages about how this SS is always crying over the fact that she and DH are not "friends". Previously, she sent messages that this SS was worried because DH and I wanted to move next door to her, so DH could stop paying child support. This SS recently told his brother that he was "disrespectful to mom" because he left "the new sweatshirt she bought you" at our house. This SS seems to not realize that DH's child support paid for some of the clothes he received, likely because BM pretends that she is paying for everything. 

Every couple of years, she will also demand a mediation to deal with "issues" that are typically non-issues or totally unspecified by her. At the mediation four years ago, she spent the entire three hours sobbing and saying "why are you doing this to me?!" to DH even though she was the one who threatened to take DH to court if he didn't agree to mediation. A week later, she told DH she was going to ignore the provision that they no longer speak on the phone and told him it would be child neglect if he refused to take her calls. 

Before the last mediation, she called DH's brother and told him that DH was so mean to her that this SS was too "traumatized" to come to our house anymore. She wanted BIL to submit an affidavit for the mediation to support reducing DH's time. She spent almost a year telling DH how traumatic it was for SS to come to our house and demanding a mediation to reduce his visitation time, only to say, "SS is fine going back to the original visitation" after three visitations on the new schedule. It was a whole year of her screaming that SS was in crisis and needed emergency counseling just to deal with seeing DH and now he's miraculously fine and happy to go back to the original schedule. Now she's complaining that DH doesn't want to spend more time with him above and beyond visitation (the same visitation that she "just had to" seek to reduce for the "good of the children").  

This SS also continues to have screaming, crying tantrums even though he is a teen. He also texts his mom demanding to go home, saying he hates DH and DH is "mean" if DH ever tries to parent. He is convinced people are out to get him all the time and when things don't go his way, he loses it and accuses DH of "hating" him. 

With regard to me, when I first met BM, I hopped out of the car with a smile on my face, ready to say hi. She gave me a perfunctory handshake and then went on to reprimand DH about something in front of the children. I later asked him, "why does your ex wife hate you so much?", to which he said "I don't know..." About a week later, she sent me a FB friend request, which I ignored. She then withdrew it four days later. Shortly thereafter, she called DH in tears wanting to know why I had rejected her FB friend request. Then she started telling DH's family that I was trying to take SSs away from her, she told them I was "aggressive", etc. At that point, I totally cut her off...I do not have time for any of that. Eight months later, her sister had a heart attack. At that point, she and DH were only speaking on the phone in emergencies, but DH took her call, assuming that he may have to pick up his children somewhere. BM quickly shifted the conversation to why hadn't I accepted her FB friend request? Why couldn't I be her friend? Again, asked in tears. I told DH that was really crazy and I was actually worried about my safety at that point. 

DH's mother is less extreme, but even when he was a child she would insult DH and tell him he wasn't good enough. She's also emotionally immature and will lash out at DH if things don't go her way. When DH told her he was getting a divorce she told him it was "the worst day of her life" and that he was "bringing shame upon the family." Mind you, DH's father was killed in a car accident 13 years before DH got a divorce...apparently long enough for MIL to forget how bad that day was and believe that DH's divorce was the worst thing that ever happened to her. Recently, MIL sent several emails out to the entire family...no one replied, but DH received a text from her saying - "didn't you see my emails?! Am I on your sh&t list?!" Right now, MIL just thinks DH is a terrible person for not "working out his differences" with BM. Same with BIL. I'm done with BIL, but I still try to be nice enough to MIL. 

quite recently hubby mentioned his frustration at sd’s and planning a mini getaway and they as usual last minute told their brother that mummy wouldn’t let them go. Hubby said if he knew this was the plan all along he would have flied overseas to spend time wih me and our toddlers. 

Thing is sds continually tell hubby all kinds of stories about their mum, 1 minute she’s on good terms with her family then its not then it is then its not and stories and drama continually change and hubby keeps quiet about it. It gives him a headache.

i told hubby spending weekends and holidays with stepbrats is a waste of quality time with my kids, like we are the ones expected to go the extra mile and be inconvenienced so they feel like the boss.

Best thing is remain non-responsive to their drama which i know is extremely hard. My dad told me people like this tend to die earlier because they’re such bitter angry people whilst the rest of us do our best to take care of ourselves and enjoy life