Spindle0516 
Thanks for sharing.
Am I making sense? Does anyone have experience with this or has anyone struggle with something along these lines? Any ideas on how to navigate this?
I have 3 siblings.
Sibling #1: Married, 2 children. I'm on civilised terms with him. We don't catch up because we're both very busy.
Sibling #2: Divorced, 2 children from first marriage (M and F within 15–20yo). I'm on civilised terms with her.
Sibling #3: I don't know what marital status, at least 1 child. I'm basically NC with him.
My husband's FOO all use the 2 kids as pawns to manipulate each other.
I know what this is like. I've had FOO members use children to cajole resource-holders to give them benefits; implicitly and explicitly.
I'll speak about my relationship with Sibling #2's 2 children (M and F within 15–20yo) from her first marriage.
Basically, we just want them to know that we love them and we are there for them.
I told both of them explicitly (almost every time I meet them) that they can approach me in person and by text; with issue or without issues.
We hope to be a haven if or when their FOO becomes people who aren't safe or loving or supportive.
My take on this is that I hope to be there for them when they have issues they struggle with. I told them both quite recently that if they think their families aren't normal, that I basically understand that and we can discuss it if they want to.
We wish we could prevent them from falling victim to the same abusive cycles as the rest of them and that we could prevent them from developing the same disorders as the rest of them.
I wish I could prevent them becoming like the disordered members around them. I look at this based on the blessings that God's given to them, rather than my role. I can only do X things to help them not have a fragmented self. I'm also limited in that I'm an uncle-figure, not a father to them.
We cannot save them from their FOO, but we desperately wish we could protect them from what they will definitely experience due to the BPD"s they will grow up around.
I wish I could protect them too. Again, this is very much based on what opportunities they have for themselves.
I look at it like this. If I have to pick a child to spend time with beyond my daily responsibilities, the "picking" order is my children, then everyone else's. If I don't have time to help X's child with their boyfriend/girlfriend/school issues, then that's just how it is.
From age 0 to about 11 are the child's main brain-formation years (along with nervous/limbic systems). It's not my job to save every child with the limited resources I have, although of course I have a desire to.
The job I've taken is consistent with the board one (for detaching); know your values, act by them, it's not your job to change others, though you can influence them accordingly, it's still their choice to act. So what this means is that I make myself available to them and let them know they can approach me if they want the help. In my view, this allows them to use their self-capacity of self-activation to pursue a resource that they think can help them. Even when that happens, I take quite a deliberate approach to coaching them (I've held an indentured faculty role at college). When they have issues in their lives, they've contacted me. Almost always so far, the issues have just been quite normal griping about school and relationships. And even though I've tried to help them understand I'm here for them for maybe 8y+ now, they only started approaching me in late teens.
So I've let them know how they can use me, but the executive functioning of their own lives is up to them and God.
Faith is a quite a bit part of a my life now, so I strongly support their walk as Christians, so I try to be more proactive in that space.
If anyone has any input / feedback on how they're dealing with nieces / nephews, me too, I'm interested in hearing your sharing.