I'm a Utah State fan. My three brothers in law are BYU fans. We all boo each other's teams and schools. When we gathered around his hospital bed to give him a blessing as his fight with cancer was coming to a close, one thing that WASN'T top of mind was the school we cheer for. I guess what I'm saying is that you shouldn't take your in-laws "BYU hating" too seriously. It does not matter...at all.