Seek the happiness of others above our own.
We owe our families the kind of relationship we can take into the presence of God. . . . We can determine to forgive quickly and fully. We can try to seek the happiness of others above our own. We can be kind in our speech. As we try to do all these things, we will invite the Holy Ghost into our families and into our lives.
Henry B. Eyring, First Counselor in the First Presidency (source)
"Testifying of God's 'eternal purposes,' the prophet Lehi taught, 'Men are, that they might have joy' (2 Nephi 2:15, 25). Many people try to find happiness and fulfillment in activities that are contrary to the Lord's commandments. Ignoring God's plan for them, they reject the only source of real happiness. They give in to the devil, who 'seeketh that all men might be miserable like unto himself' (2 Nephi 2:27). Eventually they learn the truth of Alma's warning to his son Corianton: 'Wickedness never was happiness' (Alma 41:10). . . . We will find peaceful, eternal happiness as we strive to keep the commandments, pray for strength, repent of our sins, participate in wholesome activities, and give meaningful service."
President Eyring counsels us to seek the happiness of others. The way to find lasting happiness is through the gospel. In mixed-member families, some parents or siblings don't know the gospel. Even in most whole-member families, there's probably one or two parents or siblings who aren't living gospel standards. We are called to be a "city on a hill," a lighthouse (Matthew 5:14, 3 Nephi 12:14). Lighthouses direct sailors when the waters are rough. We, too, can lead our families through rough waters, knowing that we have the true path to happiness. The Lord desires that every member of the human family return to Him, sealed in smaller family units. He wants our family sealed and living a celestial level of life. People can't live celestial if they don't know celestial. We need to teach our families, in their head and in the heart, what the gospel is and what it means. We can do this by being an example, and also talking about the gospel. We can be the one to bring our families home to Heavenly Father.
The second part of the above quote describes how we can find "peaceful, eternal happiness." Two in the list are wholesome activities and service. We can have wholesome fun with our families and serve others together. Watching movies, playing board games, going for mini golf or to the park are all ways families can bind and have fun together. Families can serve by visiting those in need, baking cookies to deliver to others, or teaching a child's friend about Jesus Christ. All of these can be done in whole- or part-member families. As families grow close together, trust is built, and we move toward a celestial level of family life.
Familiy life requires sacrifice, and the gospel requires sacrifice. Families will not be happy if everyone demands on getting what they want right away. The psalmist wrote: "I will freely sacrifice unto thee: I will praise thy name, O Lord; for it is good" (Psalm 54:6). We must be willing to sacrifice and compromise. If my brother wants to play Mouse Trap but I want to play Clue, I must be willing to sacrifice sometimes. If I want meatloaf for dinner, but the rest of my family really wants spaghetti, I might have to sacrifice. By the same token, there will be days when a brother or sister has to sacrifice - they don't get to play their game or have their preferred dinner. When that happens we should be kind and loving towards them, and appreciative of their sacrifice.