My first (and most important) suggestion is that you commit your time with your family to God in prayer. Pray for those who might be difficult; pray for those who might react in a negative way; pray especially that a spirit of love will dominate your time together.
And pray too for yourself, that you may bring peace to this gathering -- as God wants you to do. One way might be to plan a series of activities that will keep people occupied; too much free time could bring trouble. Another could be to assign duties to people so you don't have to do everything yourself -- and people will have to work together. Remember the Bible's promise: "Peacemakers who sow in peace raise a harvest of righteousness" (James 3:18).
Be prepared also to intervene and change the conversation if you see it headed in a troubling direction. More than that, ask God to help you watch what you say, and to be kind and gentle in your speech. The Bible says, "The tongue of the wise brings healing" (Proverbs 12:18).
In addition, do all you can to make this a true Christmas celebration -- that is, a celebration that focuses on Jesus Christ and His coming into the world. Before you begin eating, pause to thank God not only for your food and your family, but for Jesus Christ. Include a Christmas Eve or Christmas morning church service in your activities if you can. When we focus on Christ, our differences begin to fade.