This question goes with my last one about the second cousins.?

It is my son who is 14 and the girl is my husbands older brothers granddaughter and they get along great.They are very interested in each-other.I don't know how long it will last my cause she is 12 and he will be going into high school next year so who knows.But yes some of her immediate family seems to have a problem with it.That is not right- I keep telling them My god they are only hanging out together they aren't having or running off to be married next week.but if they were old enough for all of this what are the chances if kids were in there future?