Hi,
I just watched the talk of the Chief Rabbi of the United Kingdom Jonathan Sacks gave at the Chabad convention. I found it inspiring.
We keep a Kosher home and are very active in our local synagogue. Our oldest child is married to a Catholic, our middle is mildly interested in Judaism and our youngest has absolutely no interest.
How does one change another's thinking? How can I try to repair our family?
Answer:
Judaism in many ways is like light, a timely analogy to your situation as we just celebrated Chanukah, the festival of light. On the first night of Chanukah, we light one candle, but on the following night one light is not enough; we add a second, and on the next night a third, and so on.
Our sages teach that “One should always ascend with regard to holy matters.” The same is true with other aspects of Judaism.
Take some time to think about your current level of observance and how you can grow one step at a time. Are there local classes in Judaism that you can attend once a week? You write that your home is kosher; can you increase in your observance of Shabbat? For more ideas see our Mitzvah Minute section.
Rabbi Yosef Yitzchak Schneersohn, the sixth Chabad Rebbe wrote, “Where a lantern is placed, those who seek light gather around, for light attracts.” Our loved ones follow our example; actions speak louder than words.
Fill your home with love for Judaism and the warmth of Jewish traditions, and little by little, your children will feel the warmth and gather around to celebrate with you.

Becoming more religious is not going to heal this family; rather it is likely to drive them further apart as the strictly observant will be unable to share activities with the more liberal members of the family. Religious observance is a personal choice, but you need to face the reality of what will cause division in your family.
I know many families that remained close while one or more family members increased in religious observance. With mutual respect, sensitivity and consideration, the specific activities they do or don't do together matter less, and they find ways to connect that work for everyone.