I don't think the OP is talking about going to the family reunion looking for love.
I'm married but if I was dating someone and found out that they were a distant family member, I would keep dating them. I have family I have never met. Chances are I could be involved with a family member and never know it. Would I date a cousin or even a second cousin? I prefer that the family tree have branches so no. But finding out that the person I was dating was a distant relative wouldn't make me break off the relationship.
I'm married but if I was dating someone and found out that they were a distant family member, I would keep dating them. I have family I have never met. Chances are I could be involved with a family member and never know it. Would I date a cousin or even a second cousin? I prefer that the family tree have branches so no. But finding out that the person I was dating was a distant relative wouldn't make me break off the relationship.

I'm not sure why, as parents, you would even be thinking that way.
Some people obviously see it as a big deal, and some don't, that's the opinion I was looking for, just a topic of conversation. Odds are as they get older they would see themselves as related and it wouldn't be even something they would consider, but there is always a what if scenario. For all I know, they could grow up hating each other. Like I said, simply a conversation topic. Nothing more, nothing less.
From the brochure Getting Married in New Brunswick from Service New Brunswick: