Judging from these two words, first of all, their pronunciations are the same, but it is more troublesome to write about family happiness, while it is easier to write about family happiness. From the perspective of word-making, the word "Guan" originally meant door panels and doors, which extended the meaning of Guan, so a happy family means that when the door of the house is closed, the family is complete.
If the word "harmony" is removed from the side of the door, the word "family happiness" also means aggregation, so the meaning of the word "family happiness" is profound, which means that when the door is closed, the family will be happy.
Now, in mythology, the word family happiness is relatively easy to explain. Harmony means keep your mouth shut, which means keep your mouth shut. The extended meaning is to close it, so the happiness of family is that the family will be happy when they are combined.
Generally speaking, we see that family happiness is used in written language, such as inviting friends to dinner, in hotel invitations and oral language, and also in some festive occasions, such as marriage and New Year greetings.
Secondly, the language of China people can be divided into honorifics and honorifics usually expressed. There are strict preparations to distinguish these words, which also confuses some foreigners, such as your son, your son, me and so on. Many words can only be used when you are modest, and some words must be used when addressing others. Family happiness is such a word.
So generally speaking, family fun will appear in formal occasions or formal discourse. For example, if you want to bless others or all employees on your behalf, you can use family happiness, but if you interact with ordinary friends or some relatives and friends, you can use family happiness, which is simpler and clearer.