We can't always control how others will act, but God still can use us to bring peace to situations like this. The key is not to wait for something unpleasant to happen, but to do all you can in advance to prevent it. The Bible says, "If it is possible, as far as it depends on you, live at peace with everyone" (Romans 12:18).
What can you do? Let me suggest three things you might do; you may think of others. First, keep your guests focused on thankfulness. More than any other day of the year, Thanksgiving should be a time of remembering and rejoicing -- remembering all the good things God has given us, and rejoicing in them. Invite others to tell what they're thankful for -- and let them know you are thankful for them. Thankfulness drives out grumpiness!
Then keep them busy! Ask others to help you -- not just with dinner, but also in other ways. Not only will this keep them preoccupied, but it will make them feel needed -- and appreciated. The Bible says, "Diligent hands will rule" (Proverbs 12:24).
Finally, keep your gathering in your prayers. Pray not only that everyone will get along and there won't be any gossiping or backbiting, but that everyone will sense the presence of Christ in your home. Begin your Thanksgiving dinner with prayer also; it will set the right tone for this event. The Bible says, "Devote yourselves to prayer, being watchful and thankful" (Colossians 4:2).