After another bout of losing my temper with my DC's dad (while they were at school & over the phone) I'm looking for some more leveled ways to deal with him and his passive aggression and general undermining.
The undermining has been through out our separation which had been 6 years now (your mum won't manage on her own in the house, look at what your mums doing now, she can't keep a BF, she'll never pass her driving test, well ok she drives, but she'll be dangerous)
I feel in the main I have risen above it but my children are teens now and I can hear his words and thoughts parroted back.
A few months ago my teen DD wanted to spend a few extra days here ( she shares a room with her step sister) I agreed but it was out of the blue. From her words it transpired that after expressing she wanted to come home her dad said "so you don't love me anymore" 'You'll never come back' "your mum will turn you against me"
While here, he kept texting her (she barely replies to people anyway) and if the reply was too long he'd be "fine be like that" - resulting in me asking him not to text as she had a panic attack.
I feel like since that incident he's been working on our son (2yrs younger) spending more time with him playing video games, playing football, he is now very protective of his dad.
I've had a string of crap over the past weeks, children had covid, my relative died in Scotland and now I have covid.
He decided to take 10 days off paid from work when the children had covid. He lied and said they were with his during incubation period, they weren't and they Quarantined with me too 
He then couldn't possibly help me during the funeral, did nothing to alleviate my stress and I had to cobble some child care through other family.
I now have covid, he also can't have them easily (after taking unneeded time off as he works while I have them and lives a distance from school) but I can manage and I put a strategy in place to isolate myself I have plenty of masks and disinfectant spray for communal areas, meals are being brought in by family.
The passive aggressive messages from ex have begun, you'll all need to isolate (out of date information) my daughter called worried about covid. I talked her through everything I'd put in place to keep them safe.
Now my ex has texted to say my son is really worried about coming home, I asked if he explained about me isolating, separate bathrooms etc (we have a big house) - no he didn't just said 'you probably can't get re infected again!
Argh! In reality I have another 7 years of this shit, I know he's never gonna support my decisions, so how do I keep firm boundaries?
My concern is in times like this, his narrative will be look at your mum infecting you putting you at risk, well less a narrative more he'll tell them that or tell people that about me in front of them.
I don't come from a level headed poised world sadly, so looking for some advice to distance myself but still be civil