The Roman God family tree is very complicated, and it does not help matters that some information differs, depending on which sources you use. As far as I can make out this is how it went.

Uranus and Gaea, were parents to Saturn.
Saturn was mother to Juno, Jupiter, Neptune and Pluto.
Jupiter and Juno were brother and sister, but they married and had children. These were Juventas, Mars, and Vulcan.
Jupiter also fathered children with Leto, they were the twins Apollo and Artemis.
Saturn and Ops had children, they were Ceres and Vesta.

The Romans believed that when the world was created, it was divided into three portions which time cannot kill. Jupiter took air. Neptune took the sea. Pluto took the home of the dead, under the earth.

Gods and Goddesses
Apollo was the god of music, healing, light and truth. He is often shown playing the lyre. Romans believed he moved the sun across the sky every day, with his chariot and four horses.

Bacchus was the god of wine and parties, which made him very popular. He is usually shown looking very merry and resting on bunches of grapes.

Ceres was the goddess of the harvest, initiation, and civilization. She was also known as corn goddess, eternal mother, sorrowing mother, and grain mother. She is usually shown carrying a bundle of grain. She had a daughter called Proserpine.

Diana was goddess of the hunt, the moon, and fertility. She was both an earth goddess and a virgin goddess. She is usually portrayed with her bow and arrow, or her hunting dogs. She made up a third of a trinity with Egerion the water nymph, and Visbuis the woodland god.

Jupiter was the most important god, and ruled over them. He is the god of the sky, lightning and thunder, which is why he is normally depicted holding a thunderbolt. His temple was where official business of state was conducted, and also where executions took place.

Juno was Jupiter’s sister and also his wife. She is the goddess of women and fertility. Her symbols are the peacock and the pomegranate.

Mars was the god of war, the soldiers prayed to him for help before they went into battle. He was the strongest and most feared god after Jupiter. He was also regarded as the father of Roman people, as his son Romulus was the legendary founder of Rome. He had a wife called Belona.

Mercury was god of travellers and tradesmen. He was also the messenger of the gods, and had winged sandals and helmet so he could travel fast to wherever they sent him. His symbol is the caduceus, a staff with two snakes entwined around it, and a purse because of his connection with commerce.

Minerva was the goddess of wisdom, learning, art, crafts, and industry. Her symbol is the owl. Jupiter was father to Minerva, although she was not born in the usual way. One day Jupiter had a fierce headache that he could not get rid of, until Vulcan split his head open. Minerva jumped out, clad in armour and carrying a spear and a shield.

Neptune was the god of the sea, and his symbol is the trident.

Venus was originally the goddess of gardens and vineyards, but later on this changed. She is now regarded as the goddess of love and beauty.

Vesta was goddess of the hearth and home, she was very important to the Romans. A flame was kept burning in her temple and never allowed to go out.

Vulcan was the god of blacksmiths and craftsmanship and the underworld. His forge is supposed to be beneath Mount Etna. This is where he made weapons for the gods and heroes, and the Romans thought that if he stoked his furnace too high, the volcano would erupt.

The end of the Roman Gods
In 312AD Emperor Constantine said he received a message from the Christian god on the night before a big battle, by way of a dream. After winning that battle, he was so grateful that he made the whole empire Christian. He did such a good job of changing them that the empire stayed Christian.