When I was raising teenagers, we sat around the dinner table 4 or 5 times a week. That was in the 80's, and we laughed, listened and fervently praised God for our family which was a "yours, mine and ours" family. Ironically the two who did not share any parents were thought of as brother and sister by high school compatriots. This is true because they were only 15 months a part, and shared many mutual interests, but also amusingly, they were both blonde blue eyed, summer born kids who talked big time and laughed frequently. They did indeed seem like twins. And yet, because of the dinners together, and the group/family sense that this provided, they were "bro and sissy". This is a good thing for which with a commitment and little effort, you can accomplish - big time.