Who were the parents of Ravana?
What were the names of Ravana's brothers and sisters?
And who is the real king of Lanka? Ravana or Vibhishana?
Ravana's parents were Vishrava (son of Pulastya) and Kaikesi (daughter of Sumali and Thataka). Kaikesi had two brothers Maricha and Subahu which would effectively make them Ravana's uncles.
Ravana had six brothers and two sisters:
Kubera – the King of North direction and the Guardian of Heavenly Wealth. He was an older half-brother of Ravana: they were born to the same father by different mothers.
Vibhishana – A great follower of Rama and one of the most important characters in the Ramayana. As a minister and brother of Ravana, he spoke the truth without fear and advised Ravana to return the kidnapped Sita and uphold Dharma. Ravana not only rejected this sane advice, but also banished him from his kingdom. Vibhishana sought protection from Rama, which was granted without hesitation.
Kumbhakarna – One of the most jovial demons in Hindu history. When offered a boon by Brahma, he was tricked into asking for eternal sleep. A horrified Ravana, out of brotherly love, persuaded Brahma to amend the boon. Brahma mitigated the power of the boon by making Kumbhakarna sleep for six months and being awake for rest six months of a year (in some versions, he is awake for one day out of the year). During the war with Rama, Kumbhakarna was untimely awakened from his sleep. He tried to persuade Ravana to open negotiations with Rama and return Sita to him. But he too failed to mend the ways of Ravana. However, bound by a brother's duty, he fought on the side of Ravana and was killed in the battlefield. Before dying he met Vibhishana and blessed him for following path of righteousness.
Khara – King of Janasthan. He protected the northern kingdom of Lanka in the mainland and his kingdom bordered with the Kosala Kingdom, the kingdom of Rama. He was well known for his superior skills in warfare.he was killed by Rama.
Dushana – Viceroy of Janasthan.
Ahiravan – King of the Underworld ruled by the rakshasas by Ravana and Demon King Maya.
Kumbhini – Older sister of Ravana and the wife of the demon Madhu, King of Mathura, she was the mother of Lavanasura. She was renowned for her beauty and later retired to the sea for penance.
Surpanakha – The sister of Ravana. She was the ultimate root of the kidnapping of Sita. She was the one who instigated her brothers to wage a war against Rama.
Rāvaṇa was born to Viśravā (father) and Kaikasī (mother, a.k.a Keśinī).
This chapter of Uttarakāṇḍa of Vālmīki Rāmāyaṇa narrates the birth of Rāvaṇa, his two brothers Kumbhakarṇa & Vibhīṣaṇa, and his sister Śūrpaṇakhā.
From this blog, here's Rāvaṇa's family tree:
You can find his other family members' details in the Puranic Encyclopedia under the name Rāvaṇa.
Before Rāvaṇa, his stepbrother Kubera ruled Laṅkā. After Rāvaṇa was killed in the war, Rāma instructs Lakṣmaṇa to install Vibhīṣaṇa as the new king.
Who were the parents of Ravana?
The parents of Rāvaṇa were Viśravas and Kaikasī. Viśravas is the son of Pulastya Brahma, one of the mind born son of the creator Brahma.
What were the names of Ravana's brothers and sisters?
The lineage of Viśravas is explained in detail in Chapter 8 of Upodghata Pada of Brahmanda Purana.
38-40: Viśravas married Devavarṇinī, the daughter of Brihaspati, Puṣpotkaṭā and Vākā, the daughters of Mālyavān, Kaikasī, the daughter of Mālin. Listen to his children begot of these. Devavarṇinī gave birth to Vaiśravaṇa the eldest son.
44-46: On seeing him, his father said "This is Kubera(the ugly bodied one)". He was Kubera on account of his deformed body. He was thus marked by his name. Since he was the son of Viśravas and also due to his resemblance, he would be known by the name Vaiśravaṇa.
- Kaikasī gave birth to Rāvaṇa, Kumbhakarṇa and śūrpaṇakhā, a daughter. Vibhīṣaṇa is the fourth among her children.
55-56. Mahodara, Prahasta, Mahāpārśva and Khara were the sons of Puṣpotkaṭā. She had a daughter (named) Kumbhinasī. Also Triśiras Dūṣaṇa and Vidyujjihva the Rākṣasā are remembered as the sons of Vākā. There was a daughter named Anupālikā.
- Thus these ten Rākṣasās, the descendants of Pulastya, were of very cruel activities. They were of very terrible pursuits ever since their birth. All of these were unassailable even to the devas.
Hence from the above excerpt of Brahmanda Purana, it is clear that Rāvaṇa had thirteen siblings(10 brothers and 3 sisters). They were:
From verse 57, we know that only ten of these are of cruel activity and other four are not. But it is not mentioned who are those cruel descendants.
And who is the real king of Lanka? Ravana or Vibhishana?
Before Rāvaṇa, Kubera was the king of Lanka. After Rāvaṇa's death in the war, Vibhīṣaṇa was installed as the king of Lanka.
In addition to the other answers, it is also important to trace the lineage of Kaikasi to understand Ravana's adharmic actions.
A Pishacha (wicked ghostly cannibal) named Aj had a daughter named Jantudhanaa. She married Rakshasa (fierce cannibalistic younger son of Kashyapa and Khashaa) and had a daughter named Yatudhana. In turn, Yatudhana gave birth to Heti, Praheti and 8 others [Ref: Brahmanda Purana Upodghaata paada 7.43-90]. All her descendants are called Yatudhana-Rakshasas.
Heti’s descendants were Malyavan, Sumali and Mali. Kaikasi (daughter of Yatudhana-Rakshasa Sumali) married Vishrava (son of the pious Rishi Pulastya). Their children were Ravana, Kumbhakarana, Surphanka and Vibhishana [Ref: Ramayana 7.4-5, 7.9]. They and their descendants were the Kaikasi-Rakshasas or simply Rakshasas.
Thus, Ravana was a son of a Brahmin father and a Yatudhana-Rakshasa (hybrid descendant of a Pishacha and a Rakshasa) mother.
Source: 'Essence of the Fifth Veda' by Gaurang Damani page 14.