Sadly, conflict between members of the same family is almost as old as the human race. Cain -- Adam and Eve's first son -- became consumed with jealousy and anger toward his brother, Abel, and it led eventually to the first murder (see Genesis 4:1-16).
What is the problem? The problem is that down inside we all want to live only for ourselves and our happiness -- and when we believe someone is going to keep us from reaching that goal, the result is conflict. And the closer we are to someone (such as being in the same family), the sharper the conflict. The Bible puts it this way: "What causes fights and quarrels among you? Don't they come from your desires that battle within you?" (James 4:1).
I'm thankful you want to bring peace to your family -- and I believe God will honor your desire, as you seek His help. What can you do? First, pray consistently for your siblings -- not only that they'll overcome their hostile or indifferent feelings and grow closer to each other, but also that they'll come to know Jesus Christ. You can't change them, but God can -- just as He has changed you.
Then reach out to them. Christmas is approaching; why not invite at least one family for Christmas dinner, or do something else that shows you care. In addition, ask God to help you share -- humbly and yet boldly -- what Jesus Christ has done in your life. God bless you.