My future brother-in-law and his ex-wife are acting like children. Their divorce was finalized only recently, yet from the beginning they’ve both been seeking their next relationship, putting the emotional and psychological needs of their school-age children, second.
Both children have exhibited anger, distraction and hostility, which neither parent is addressing.
Worse, the mother is communicating destructive things about her
ex-husband to her children!
Neither provides consistent boundaries, responsibilities, follow through nor consequences. Both are so caught up in budding romances that they let the grandparents take care of the kids, or allow incessant TV watching and video games.
How do you diplomatically tell them that their personal, short-term pleasure is jeopardizing the long-term future of their children?

- Frustrated

The fact that going through a divorce is tough (even for the bystanders) is a cliché; what’s less understood is that each person involved is going through it differently, presenting their own mask of coping, and submerging their own pain.
Your adult relatives are embracing relationships because they think that’s what will return them to “normalcy” fastest. It’s a common reaction to the years of repressed, then unleashed anger, frustration, hurt. If they can just get a new partner, they think, they’ll not have failed themselves or anyone else, life will return to a happy state.
The kids? They’re obviously acting out, and the parents may honestly think they should let them “get it out of their system,” awhile.
Or, they indulge them, hoping that once the family is “settled,” they’ll focus on the fallout.
You’re correct that this is psychologically harmful to children, who need special care, comfort and communication throughout this time.
One book to give as a gift from a caring relative, is Parenting through Crisis by Barbara Coloroso. As it’s title suggests, it works on the basis of no blame, and kindly implies that you believe these parents are still conscious of their role.

Throughout our seven years together, my boyfriend’s parents tried to break us up – they’re verbally and physically abusive, wanting to control both our lives. They’ve gossiped about me, made racist comments about my ethnicity, and tried to get their son to drop school.
My mother died from cancer several months ago. When my boyfriend would help my family, his parents complained that he was spending too much time with us. Eventually, they kicked him out of their house.
We now live in an apartment, he’s cut off contact, but they still call him bi-weekly. He didn’t reveal we bought an investment property or his new job, because whenever he benefited financially they believed they deserved a share.
Although he claims he hates them, I know he’s just hurt and still loves them. Whenever I discuss reconciliation he reminds me that we’re struggling because they kicked him out, and going back would defeat what he’s accomplished.
Is there a solution to this?

- Confused

Family deserves a second chance, but not always a third, if the relationship remains toxic.
Reconciliation can only be based on you two holding your position as an independent adult couple. He would not “go back;” rather, he’d offer to see them. And he would set limits on further contact: no bad-mouthing you, no criticisms, no controls (and no money-grabs, except in an emergency).
If they want a relationship, they need to respect your separate life from them. Next, you’d visit together.
You’ll know soon enough if they can adjust, OR if you two feel strong enough to tolerate some of their nonsense.

I’ve been in a great relationship, living together six years; he has three adult children and grandchildren from a 30-year marriage.
His ex-wife, who’s re-married, still socializes with his siblings and elderly parents. My guy refuses to inform her of boundaries because it’ll upset their adult children, affecting his relationship with them.
I resent that she doesn’t respect my position and pretends I don’t exist.
My trust and closeness with his family has weakened because of this.

- Annoyed

Get over it. You do exist, and there’s no competition here. After 30 years, SHE has real relationships with his family; after six years, YOU are clearly his full-time partner. Yet your attitude smacks of insecurity, and you want this man to back you despite that it’ll cause him heartache.
Meanwhile, the relatives don’t even consider this woman as “his” anymore… they’re part of a long-term extended family scene. Get into it, too.