Dual-core family: refers to the fact that both spouses were the "core" (only children) in their families before marriage, and they did not know that they should act in a "non-core" manner after marriage, so two "cores" appeared in the family. Which of the following belong to dual-core families? ['The newly-married Wang and Liu still have the stubborn personality of the only child and refuse to give up.', 'During the Chinese New Year, the couples invited their brothers and sisters to reunite at home.', 'Xiao Wang and Xiao Li are both only children. After the two set up a family, the husband and wife sang with each other and treated each other as guests.', "Xiao Xu feels a bit depressed and unhappy about the beauty of Jiao's wife, and the sweetness of the wedding is gradually diminishing."]