Hi Cat,
what popped into my head when I read your post was this, fwiw:
I think there's no "rule" about who's safe to get to know. Some people with Nparents turn out kind, some turn out N-ish. Some...somewhere in between.
So I think what works best is, rather than thinking of these young people as categories, decide that your own observations of who they are are the most important thing.
So...secondly, rather than deciding on principle that you'd "really like to get to know them" -- how about telling yourself, "I'd like to spend enough time around them, and observe carefully, and listen to my intuition, and trust my gut feelings...and based on how I FEEL around them and based on what I SEE of their behavior...find out if I LIKE what I know so far. And that will guide me as to whether I really actually would "like" to get to know them. (Or have my kids do so, etc.)
You can't control it if your kids are attracted to their cousins, of course. But you CAN create protective boundaries and limits and cautions for yourself...until you feel it's safe and happy to let your guard down. Or not. Who knows? You might really like one of them and not the other, for example. See them as actual people with personalities you intend to observe and evaluate...and respond to the reality of what you notice, not just to sentiment. Might turn out great -- and in fact the result will be great no matter what it is, if you proceed this way. Because you'll be experiencing self-care, self-respect, all that healthy stuff.
Let your good judgment, and your experiences, and your inner knowledge and observations...be the guide for what people you want to invite more closely into your life. NOT the fact that they are blood relatives.
Sounds brutal, but that's what I beliieve is healthful...
Help any?
love,
Hops