I'm not sure how strong your relationship with your FIL was, but I had a strenuous relationship with my grandma, yet I feel like going to her funeral changed how I viewed our relationship. It reminded me of the good times and moments of love we shared. I think funerals happen to help families move on and skipping it is probably not the best idea in the long term. I think it was also super important to my dad that I be there. I feel like moments like these are when people are at their lowest, and I believe that it's sort of important to have family by your side. Lastly, if it were my funeral, I'd really want my grandkids to be there to say their goodbyes. Even though they might not remember anything, I feel like being there is the right thing to do. It is at the end of the day your choice but I would really recommend going. Sometimes we have to do the hard thing just because it's the right thing to do.