It might be the first time you've seen your sister since that argument last summer. You might get together once a year with your frosty in-laws. One acquaintance calls the Christmas Eve dinner "the fight before Christmas."
Conflict doesn’t mean the end of your remarriage, and can actually make it stronger. There are always going to be disagreements; you cannot avoid them entirely. What you can do, however, is become skilled at recovering from disputes by talking about your perspectives afterwards.