Lack of unity in family is a big problem today. We have so many materialistic things which money can acquire but all wealth cannot buy unity in family. Here is a mantra for unity in family.
Mantra - ॐ पार्वतीपतये नमः
Om Parvatipataye Namah
Unity in family can happen only when the important male and female members think alike.
Chant the mantra daily in the morning along with sunrise. Apart from chanting the mantra, you should read the Ramayana daily especially the Bala Kanda and the Sundarakanda.