There are different ideologies about the concept of God in Hinduism. God is One, yet many according to their religious norms. There are different gods like Brahma, Shiva and Vishnu; there are three main ones. The rest are linked with these three gods, or there are different avatars of these gods. Here is the family tree that describes the relationships of the gods.
Brahma, Vishnu and Shiva
Brahma (the Creator) has the ultimate power and is respected by the Hindus the most. He marries Saraswati (the goddess of Arts and Knowledge). Brahma's powers and cosmic role are deeply described in the Hindu scriptures.
Vishnu is considered to be the preserver and protector in the Hindu religion. He married Lakhsmi (the goddess of wealth and prosperity).
According to the Hindu religion, the primary role of Vishnu is to create balance in the universe. There are different Avatars of Vishnu as well.
Shiva is the Transformer or Destroyer. He was married to Parvati, Sati, Durga and Kali. They are considered to be the goddesses having different avatars.
According to the Hindu scripture, Shiva's role is to destroy the universe and begin anew. His intention is not observed as evil according to Hindu philosophy, as Hindus think of destruction as a transformation to a new world.
Brahma and Saraswati
Now, the family extends from these three major gods. Brahma and Saraswati have few children but are not well known and are mentioned in different holy books of Hinduism. Brahma is considered to be the Father of all gods.
Vishnu and Lakshmi
There is not a lot of information written in Hindu books about the children of Vishnu and Lakshmi. But there are different avatars, including Rama and Krishna. Rama married Sita (the avatar of Lakshmi). At the same time, Krishna had many wives, including Rukmani and Satyabhama.
Shiva and his Wives
There is a lot written about the wives of Shiva. There are different levels in them as well, but Parvati is the one whom he loved the most and had children with. Ganesha (Remover of obstacles) and Kartikeya (Commander of the divine army). Ganesha has married Riddhi and Siddhi.
The Goddess Aditi
Aditi is considered to be the mother of the Gods. She gave birth to a lot of Gods, including Mitra, Varuna, Aryaman, Bhaga, Dasha, Amsa, Tavaster and Surya (the god of the Sun). Rudra, her husband, himself, is considered a God in the Hindu scriptures. Surya, her son, is married to Saranyu. He has two children, Yama and Yami.
According to the Hindu scriptures, there is a lot we can observe regarding the concept of gods and their roles. Vedas are known to be the most authentic book, and all the details about the gods are mentioned there as well.