I definitely understand the temptation to say something to your sister — to try to stop her from making what seems like a really stupid, juvenile mistake — but is there any part of you that thinks she’d actually listen to you? If so, then go for it. But keep in mind that by doing so, you run the risk of alienating yourself from her and her children, which is a pretty big risk when you consider that you may be one of few stable adults in their lives. If, for your own sanity, you feel you have to speak up before your sister elopes, perhaps a simple, “Are you sure you’ve thought this through? Do you think it’s the best decision for the kids?” might suffice. The key is not to engage her if she retaliates with an argument or gets defensive. Say just enough to let her know you don’t 100% approve and just enough to give her a little food for thought and leave it at that. Saying any more isn’t going to accomplish anything but drive a wedge between you, and that’s not something you want.
As for your sister’s kids, you can support them by being as present in their lives as you’re able to and by modeling what appropriate, responsible behavior looks like. Kids from much worse backgrounds who have had no role models growing up have gone on to have happy, well-adjusted adult lives, so there’s no reason your sister’s kids aren’t capable of the same. They’ll be better positioned for a successful transition into adulthood if they have at least one mentor in their lives who loves them and provides a model of stability. So, be that for them if you can. You may not be able to stop their mother from being crazy, but you can be the sane one in their lives. And that’s better than a lot of children have.
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