Does she communicated with your SO? Let them sort things out between them. Either way, step back, stop doing anything for her kids and stop caring what she says or thinks. Not your problem. 

Our HCBM initially wanted to communicate with me and DH; we thought she was finally trying to coparent for once. Boy was I wrong! She was just trying to get her new GF into the "coparenting" dynamic and then after she was successful, she pulled all the same tactics yours does, all while kicking me and DH out of the "coparenting" and letting her GF take over DH's role. She then told my DH that they "coparented so much better before I came along." In reality, BM abused and gaslit DH for years and when I started dating him, I pointed the abuse out and help him set boundaries. 

The final straw for me was when SS9 (who was 6 at the time) asked me to make some bags for a him and a few of his friends. SS helped me make these really cool bags that could hold all their sports stuff. BM later texted me saying that SS told her I forced him to make the bags and that it put her in a bad position, as not every team member would get one and clearly I was intentionally trying to make her look bad. I told her that she/SS did not have to give the kids the bags then, but BM would have to explain why to SS. BM then tried to gaslight me saying that I appeared upset and she kept harassing me, even when I stopped responding, she kept texting. That day, I blocked BM's number, GF's number, and their emails and I told DH that he was to handle all communication with BM. I was done.

It has been over 2 years now since I have communicated or saw BM. I still have her and GF blocked on all platforms. BM has tried to get me to engage by emailing DH about me. BM tried to get me to engage last summer by claiming I helped facilitate DH's "physical abuse" of SS via Nerf gun and then prevented SS from reporting said abuse. I still did not engage because engagement and drama is exactly what she wants. I could care less what BM or GF thinks of me because I finally realized that they are toxic and will never like me anyways. You are 100% right, you are damned if you do and damned if you don't, so it's just better to not. 

In normal and rational situations- being able to keep all parents and step parents in a group text and let everyone know at once what is going on, makes total sense. It is easy with coordiation and communication.

However, you wouldn't be here if you were dealing with a sane person. You are in a high conflict situation and one that you don't need to be in. So, remove yourself from the stress and tell your husband to deal with his ex. You can still be a good SM and good to the kids without ever having to speak a word to BM.

1.) Disspell any lies heard from the kids. Ideally, your SO would do this, and provide any proof they have. There is no reason to involve kids in adult matters, but if BM lies, you're well within your rights to defend yourself with the truth.

2.) Don't communicate with BM. Block her number, email, social media, etc. If there is an emergency, she can contact your SO and they can handle it as they see fit.

3.) If the kids are being rude, disengage from them. Then tell your SO how they are behaving. If your SO says they don't want to hear about it, tell them they don't have a choice; these are their kids and their responsibility, so they need to address it.

4.) If BM is lying and it is impacting you socially, financially, etc then seek out an attorney to send her a cease and desist. If she continues, take legal action. If she is physically harassing you, get a restraining order.

I don't interact with ET (BM). When the boys used to be confused by something ET said, DH would tell them the truth. ET burns her own bridges and doesn't need my help setting them ablaze.

I find when I and DH Ignore HC toxic BM tantrum's it's the best thing. She also has an agenda to make our lives insanely miserable and hard. We just try really damn hard to not allow it. I leave EVERYTHING to do with her and the SK's to my DH. I don't have a DH issue though, so it works for me to disengage and make him handle it. 
Unfortunately this toxic BM I deal with uses her children as pawns to manipulate and it's very hard to try and protect them. We just ensure that SD has nothing to go on, 'reporting' back to Toxic BM. I have had to work on my emotions and tolerance over the years with BM and SD. It's not been easy, but with a DH that has your back it's manageable. 

Toxic Troll BM likes to go on smear campaigns and trash-talk us to our community. It sucks, but lines have been drawn and I have had to do battle.

Block her on all social media.

So must ignore anything that doesnt have to do with skids.

The only thing that has worked for me is cutting her off entirely, which has also meant keeping DH's family at arm's length because they are her enablers.