My father took me to BYU games as a kid. He was a BYU alum, so it was natural, and when I was small, I cheered for BYU because he did.
I went to Utah and the school treated me very, very well. While I was there, I became a natural fan of my own school's sporting events and attended them and became a natural Utah fan. That was my extended family and alma mater.
And... I reciprocated by now getting my father tickets to Utah events and coming in to attend them with him.
We go to each other's events. We follow both teams. He's a BYU fan. I'm a Utah fan. When there's a rivalry game, we call each other and laugh a lot as we watch it, and as we discuss the outcome.
They like something, and it's as (relatively) wholesome (for the modern world) as Football. That's thanks to you. The other school they like is close enough that you can easily share that with them, too.
Don't let the color of the uniform ruin fun time that you spend with your family, or alienate you from your young family members (or vice versa). Sheesh. Family is everything. Stay involved, embrace it, and make them a deal that you'll go to their games if they'll go with you to your games, and you can all rib each other afterward, depending on who wins.
With all the forces acting against family these days, you're going to reject family time and goodwill, not to mention a lot of potential good times, based on the this? Sheesh.