my sister and her boyfriend

My sister and her boyfriend are coming "home" for Christmas. Which is really surprising she lives 2 hours away from my husband and I and my mom and dad(we live 2 blocks away from my mom and dad in our own house). Since Christmas is on a Sunday we were planning on going to church (like we do every Sunday) but my sister is throwing a huge fit about us going because she's going to be there early in the AM and she won't go with us and therefor doesn't wanna go.. so we decided that we will not go this Sunday just because we didn't want a fight over the holidays.. so my dad decided we will have church at home and so he's going to do the message and my moms doing a devotion and I'm coming to play the piano and do music.. my sister is currently unaware of this and I'm afraid she is going to be mad when she gets here.. she is a Christian she used to go to church every Sunday before she got with her current boyfriend.. her current boyfriend smokes pot(which is fine except it turns him into a complete jerk) , he's also just gotten his 4th DUI and he doesn't go to church or like church.. it's causing me serious anxiety :( ugh just wanted to vent to someone who understands why we still wanna "have church".