As I have written in my earlier articles about the Dynasties of India,there were two primary ones, Suryavansh,Solar Dynasty and Chandravansh,Lunar Dynasty. Both dynasties had sprung from Vaiwaswatha Manu. From the Suryavansh,founded by Ikshvaku, son of Manu came the Chandravansh.
Chandravansh, Lunar Dynasty gave rise to other Dynasties like Yadava or Yadu Dynasty.
Nahusha of Lunar Dynasty was the grandson of Purururavas of Lunar Dynasty.
Nashusha married Ashokasundari, Daughter vof Shiva ,Parvati
So Nashusha was the son in-law of Siva and Parvati.
As Nahusha is from Chandravansh,Lunar Dynasty, Siva’s daughter belongs to Chandravansh.
Krishna belongs Yadava Dynasty,which is an offshoot of Lunar Dynasty.
And Lunar Dynasty Dynasty is from Solar Dynasty to which Sri Rama belongs.
Therefore, Ashokasundari, daughter of Siva and Parvati is related to Rama and Krishna by matrimonial alliance.
So are Siva and Parvati related to Rama and Krishna.
*Some may not like Siva being called a Human being. I too share the idea. However, the term Siva does not refer to a person but it means ‘auspiciousness’.Siva is described as Adi Yogi,the First Yogi, who practiced the Vaasi Yoga. Kindly read my articles Siva a Human being,Siva worship precedes Sanatana Dharm, and Vaasi Yoga‘
‘Nahusha (Sanskrit: नहुष) was a king of the Aila dynasty (Lunar dynasty) and the 3,698,256th Indra. He was the son of Āyu, the eldest son of Pururavas and Prabha, the daughter of Svarbhānu. Nahusha reigned from Pratishthana. He married Viraja, the daughter of the Pitrs. They had six or seven sons, according to different Puranas. His eldest son Yati became a muni (ascetic). He was succeeded by his second son Yayati.
In another variation of his story, he is said to have married Ashokasundari, a regional goddess who is said to be daughter of Shiva and Parvati and is said to have given birth to Yayati and a hundred daughters of Nahusha.
Reference and citation https://en.m.wikipedia.org/wiki/Nahusha
‘Ashokasundari (Sanskrit: अशोकसुंदरी, Aśokasundarī) or Ashoka Sundari, is a goddess and the daughter of Shiva and Parvati in Hinduism. She gives blessings beauty and luxury. She is referenced to in the Padma Purana (पद्म पुराण), which narrates her story.
The birth of Ashokasundari is recorded in the .Padma Purana. In one of the variants of the tale of Nahusha, Parvati once requested Shiva to take her to the most beautiful garden in the world. As per her wishes, Shiva took her to Nandanvana, where Parvati saw a tree known as Kalpavriksha which could fulfill any wish. Since Kartikeya, the son of Parvati, had grown up and left Kailash, as a mother it caused immense grief and loneliness to Parvati. She asked for a daughter from the wish-fulfilling tree to get rid of her loneliness. Her wish was granted and Ashokasundari was born. Parvati promised that she would marry according to her destiny Nahusha of the lunar dynasty, who would be equal to Indra, the king of heaven. Once, Ashokasundari was roaming in Nandanvana with her maids, a rakshasa (demon) called Hunda saw her and fell in love with her. However, the goddess rejected the advances of the demon and informed him about her destiny to marry Nahusha. Hunda disguised himself as a widow, whose husband was killed by him, and asked Ashokasundari to accompany her to her hermitage. The goddess went with the disguised demon and reached his palace. She came to know of his treachery and cursed him to be killed by Nahusha and escaped to her parents’ abode Mount Kailash. Hunda kidnaps the infant Nahusha from his palace, however, he is rescued by a maid of Hunda and given under the sage Vashistha’s care. After a few years, Nahusha grows up and understands about his destiny to kill Hunda. Hunda abducts Ashokasundari and tells her that he had killed Nahusha. The goddess was consoled by a Kinnara couple who informed her of Nahusha’s wellbeing and prophesied that she would mother a powerful son called Yayati and a hundred beautiful daughters. Nahusha fought Hunda and defeated him after a fierce battle and rescued Ashokasundari, whom he married. Over course of time, in absence of Indra, Nahusha was temporarily made the regent of heaven’
Reference and citations.