When I was first starting a relationship with m now DH, HCBM told her kids that I have no eyebrows (I do but they are blonde) and look like I am pregnant (Im overweight at 5'5" 160, and she is 5'3" at 220).

This typically happens in the beginning, when there are issus and its a high conflict situation.

Many men are cowards because they believe the BM has this huge power over them. If there is a custody order in place, she cannot withhold, or she will be held in contempt.

Alienation is common with high conflict parents. Its what they do.There are a host of differing techniques, all designed to make it so that the mother is revered above the Step parent, and step is treated badly.

Me and my eyebrows, owevr, occasionally get an "I love you" from munchkin sd13. It took a lot of time, because she was/is in a big loyalty bind where her mother would get very upset when I was mentioned. To the point of crying.

Thats a tough one to battle. Your SO needs to step up to the plate, and back you up.

SS would be not allowed in my home with a mouth like that.  Your DH has to see him outside the home until he learns to be a person.  This is DH fault for not parenting his kid and making him respect you. SS does not have to like you but he must respect you and your home. 

Disengage from SS.  Don’t do anything for him.  No money. No cooking, No cleaning. No going anyplace with him. As out to dinner, or Vacation,  

If your SO (I hope you aren't married) can't protect you from his ex and his son, then yes, you are in the wrong situation. IMO, this step thing only works long term if he can do that.  You don't deserve to be mistreated, and you DO deserve to have a partner who is more afraid of losing you than he is of his ex-wife and kid.

BM put thoughts into SD's head that I was a gold digger and only dating DH for his money (he's not rich by any stretch of the imagination). All our finances are separate, I buy anything for myself with my own money, oh and, I work. Not to mention, BM has zero clue what kind of family I come from so her accusations are laughable.

IMO it's jealousy and trying to make the SM look bad. 

saying bad thing shows no respect.  That is your SO fault for letting that happen

The fact that BM is taking the time and energy to even post about you on Instagram says a lot but you also "looking" for it shows that you care and you shouldn't. What she thinks of you is not your problem or concern. The issue you have here is being with a man that lacks  the balls to stand up for you and I personally could not be with a man like that.

I feel you. In my opinion, one of the most difficult things about being a stepmother is being expected to be a non-entity in your own home and being expected to just put up with abuse with a smile on your face, because you are the interloper. 

In my case, I cut BM off entirely after she accused me of telling her children that I want DH to move next door to her so he could stop paying child support and that I was trying to take her children away from her. I can only imagine what she's told SSs about me. She is constantly telling them that DH and I hate her, even though we barely interact with her, but because she's not treated as the queen she thinks she is, she takes total offense. She has now successfully convinced DH's family that her relationship with DH was great before he met me and now it has "deteriorated". DH's family seems to forget that she used to call him a deadbeat dad, garbage, someone who doesn't care about this children...and on and on and on...long before he met me. Also, have any of them ever had a conversation with me about this? No. Have any of them questioned why her gripes are always about her and never have anything to do with the children? No. DH's brother pictures himself as the "savior" who has to step in and protect SSs because DH is not "respectful" enough to BM. 

It's caused a real rift between me and my DH because I do feel as if he's allowed me to be the bad guy, because he's too afraid to stand up to BM or his family. He tells me that he's used to being treated that way himself, so he doesn't see the big deal. However, I will never feel like a family with him and SSs if I am facing constant criticism, bullying, and meddling from BM and DH's family. 

I cringe as I write this because people used to say this to me and it did not help me at all. But as the years have gone by and I’ve looked at the lives of people who used to make fun of me or hurt me, I realize how TRUE it is about “what comes around, goes around” or “karma”.  

The girl that used to puff out her cheeks like a chipmunk when I walked by is now on steroids and her face is as big as a basketball. 

The guy who used to make fun of me because of how my mom dressed, well, he’s now dressed in an all orange prison suit. 

The girl who made made fun of my unibrow now has no eyebrows from chemotherapy 

My ex who used to have 2 boys and ended up cheating on me with the BM and ultimately left me for her “for the family” now has 2 more kids with her, twins. Their 2nd chance at a relationship only lasted 6 months, but now he’s paying for 2 more kids and looks broke and miserable as hell. 

On the flip side, the guy I dumped for being a lifelong college student is now a successful tax attorney and CPA. Lol.  

Sooo my dear, just take the high road. You’ll look much classier if you don’t give her any energy. If Skids tell you something negative that she says about you, tell them her opinion means nothing. 

You take a zero tolerance stance and you confront it.  What ever it takes to bare BM's ass, get her out of your head, give your DH and SS clarithy on the facts regarding the toxic womb donor, and keep her under the slime covered rock she occupies in the shallow and polluted end of your SS's gene pool.

Toxic should never go unconfronted.

Make destroying BM your favorite hobby. And have fun.