Ganesh's Birth
Goddess Parvati created Ganesh out of turmeric one day so that he could guard the door while she took a bath.
Lord Shiva came home and, not knowing Ganesh was his "newborn son," was furious at him for not letting him in and severed his head.
Distraught upon learning his identity, Shiva brought the boy back to life by replacing his head with that of an elephant.
Kartikeya
Ganesh had a brother but it is unclear who was the eldest brother between the two. Kartikeya (Skanda in Sanskrit or Murugan in Tamil) is known to be the God of War, and widely revered in southern India.
The two brothers had a classic sibling rivalry growing up, including a race around the world.
Ganesh is also believed to have other siblings in some parts of India. For example, some legends say he has four additional brothers like Sukesh, Jalandhar, Aiyappa and Bhuma.
While other parts of India (primarily South India) also believe Ganesh has a sister named Ashok Sundari.
Riddhi & Siddhi
As Ganesh grew older, there were different accounts of his "romantic" life.
Some texts believe him to have been celibate, while other texts associate him with two wives, Riddhi (who represents prosperity) and Siddhi (who represents spirituality).
Shubh & Labha
Ganesh had two children, one with each of his wives.
The son he had with Riddhi was named Shubh and is associated with prosperity. In some areas of India, he is also named “Kshema.”
Shubh’s brother -- born to Labha and Ganesh -- was named Labha and is associated with profit.
Santoshi
Ganesh’s daughter Santoshi came as a result of his 2 sons wishing for a sister with whom to celebrate Raksha Bandhan.
They witnessed Ganesh performing the ceremony and wished for a sister of their name, and so he created Santoshi from flames.