I have e been trying to tell my in law the sme thing. He's a Christian but his church, Church of Christ, don’t observe the Christmas celebation.
As much as he tries to discourage his children from making Christmas a big deal, his children don't listen.
He had no choice but to allow his children celebrate with us. His wife, my sister was Catholic and Christmas is always celebrate in our family.
I hope you enjoy the festivity with your sons.