I was raised Catholic but "fell away" at age nine when the pastor informed me that my salvation may be in question "as the product of an illegitimate union."
So you might understand that ever since then I've been skeptical of organized religion on the whole.
Dad was raised with an atheist father and a baptist mother. My grandfather passed long before I was around. Dad never had a Christmas until my oldest brother's first one. Grandpa Coon was told by my mom to join or get out. Gramps joined the party, though not the belief system.
How'd Gramps & Grandma reconcile their different beliefs? Don't believe they ever did or that it ever mattered. But it did produce a quote from her that I absolutely love...regardless of belief. Regarding his lack of belief, in the context of their own kids, Grandma said "I suppose he thinks his little thing made these kids all by itself."
My own fall away was cemented in a CCD conversation with a nun who agreed with my points of skepticism and was justified in taking the walk. Mom never said anything. Dad asked if I felt satisfied hurting her with my lack of catholicism which amused me since I truly believe he was an atheist himself.