All communication with her is through Our Family Wizard.  DH doesn't get notifications, so we don't get peppered with her BS.  He has to decide to go look to see what's there.

She's not allowed on our property.  Seriously, she has been warned.  If she does it again, I will have it on video and I will have her cited.

We have a *tight* CO.  She has to drop the children off for parenting time (because that way they "have her permission" to be with Dad.  Did I mention she's an alienator?) Holidays are spelled out with days and start/end times.  It's 10 pages of rules for them to follow.

DH has lots of boundaries, too.  He will not interact with BM.  We don't attend/participate in extracurriculars, doctor's appointments, etc.  It's just not worth it for us.  And he's explained to the skids why he's not there.

I don't interact with her at all, either.

1. Communication is limited to email and kid related things only. The only real exception to this is when BM is suppose to update DH on her personal life details like change of job, living address and phone number. She doesn't really do this so I guess it doesn't really matter anyway.

2. Exchanges are prepared for completely. DH is outside waiting for SS when he gets home or SS has his shoes on ready to leave with BM on pick ups. Nothing goes back and forth. He goes in his school uniform on Fridays and she returns in him that because why the heck would she need them?! He goes in the shoes she bought him, a pair of shoes she insisted he said he cried over and wanted to wear to school but have long since been tossed into his closet by him because he prefers his nike slip ons from last year (Because she has strongly encouraged him to wear slip ons instead of lace up shoes because she didn't want to deal with tying his shoe laces, even converse sneakers she bought for him she rethreaded so he could slip them on and off without tying) 

3. DH has completely shut her down every single time she has ever tried to bring me up in a conversation or argument as well as called her out on emailing/texting/messaging me about this that have to do with SS as I am not his parent nor on the Custody Order. She is a narcissist so she will seek out the path of least resistance when she wants something and that would be me, but any other time I am a horrible person trying to take over her claim to motherhood and torturing her golden child. 

4. In the custody order it says that SS must have reasonible access to his other parent. While BM has blocked me and DH from SS on "her" time because she has caught him facetiming and calling us when she wasn't around to hoover, BM does get to talk to SS once a week. DH set up a time (well before bed time because she would get him all upset when he was a toddler) and she could call. If she forgot which she has gone months of forgetting then he will take the call then next day if we aren't doing something as a family. BM has recently told people that he HAS to do this but its not true. He has to let SS call her if SS asks but he never does..but again a narcissist would never believe they are not being thought about by their prodigeny. 

I think those are all of our highlights except for this last one that is more important than any of the other combined. Do not do favors. Do not swap time or try to be the easy going, trying to make it work and do what's best for the kid type because that is how your SO gets screwed out of his time. BM is the queen favors and if DH gives in to a little one she will steady increase her favors. She will keep asking for more and more and when he eventually tells her "no" then all of a sudden he doesn't know how to coparent and he is hurting his child, etc. Well if you set the precedence that favors are only for important events i.e. marriage, funerals, etc then she won't keep asking or expecting him to give in any and every time. 

My stepkids are grown now but when they were minors ours were:

BM was only allowed to call DH's cell phone. This was after she called our house (back when we still had a landline) before 7 am one time and mocked me for still being asleep. Yes bitch, I don't have to get up that early, don't f-ing call here at the crack of dawn. She also was never allowed to have my cell or email address.

BM was  not allowed in our house. I was gracious when we had our first apartment together and let her come in to see her kids' room but I told DH that B isn't allowed in our room.  I didn't ever allow her in again and after awhile I told DH I didn't even want her on my front porch. SS lives with us now (for the past 8 years) and she has not been allowed over once. SS needed help with his car once and his stepdad had some friend with a shop near us that was going to fix it. We told SS his stepdad was not allowed on our property, he could pick him up out front. I don't allow a-holes who have talked sh-t on my DH to even come on my driveway.

these days BM is blocked and was told after my younger SK graduated high school that there was no reason for her to ever speak to DH again. It's been 6 blissful BM free years!

About a year after I met my now DH, he would sometimes stay at my apartment. He had a pager back then that she used to contact him. He once called her back from my landline phone. She took it upon herself to start calling my apartment, in a hostile tone asking for him (she had never met me at that point). After the second time she did that, I told her I didn't mind her calling but if she could not act civil, she had to go back to paging him and that he didn't even live there. She changed her tone.

Then when SD lived with us for 6 months at 15, she would call our landline every other day still trying to spread her venom. I told her she was not going to continue to poison SD on our dime and blocked her number and my DH gave my SD certain days for her to use his cell to call BM. My DH was pretty good at either ignoring BM or putting her in her place. I however, had to put a stop to that.

All communication is done via email, unless it’s a medical emergency. No voice messages. No texting. 

We live on the other side of the U.S., so we don’t have to face her, but when we did it was in the court order that drop offs/pick ups had to be done in a very public place with cameras. Yeah, BM was that volatile and physically abusive. Good times. 

DH discouraged any phone calls, but when NPD BM did call, he'd ring off the MOMENT she raised her voice to him.  I got call screening for our landline and if she ever phoned I'd never pick up.  After a few years of this she only ever called DH's mobile. She has never known my mobile phone number.   By the time the SDs were in their mid teens, virtually all communication was through them rather than direct.