What is the story of Nara and Narayana's brothers Hari and Krishna?

Question

As I discuss in this question, one of the most prominent incarnations of Vishnu in ancient times was the sage Narayana, twin brother of the sage Nara and son of Yama god of death. Nara and Narayana were famous for engaging in Tapasya (deep meditation) in Badrikashrama, and in the time of the Mahabharata they were reborn as Arjuna and Krishna. In any case, apparently Narayana carried out a five-night (Pancharatra) Yagna and then became the entire universe, so people started following the so-called Pancharatra texts, scriptures originating from Narayana himself which gave detailed procedures for worshipping him. As I discuss in this question, the Pancharatra texts were important in the development of Vaishnavism. Among the oldest Pancharatra texts are the Satvata Samhita, the Paushkara Samhita, and the Jayakhya Samhita.

But there's a Pancharatra text even older than these, and it is found within the Mahabharata! Most people only know about the Bhagavad Gita, an 18-chapter religious discourse between Krishna and Arjuna found in the beginning of the Bhishma Parva of the Mahabharata. But there is another 18-chapter religious discourse found at the end of the Shanti Parva of the Mahabharata, the Narayaniya. It is a Pancharatra text which takes the form of a dialogue between Yudhishtira and Bhishma as the latter is lying on the battlefield of Kurukshetra, and Yudhishtira asks him questions about the importance of worshipping Narayana/Vishnu. (It goes from this chapter to this chapter in the Shanti Parva; apparently the Bhagavad Gita and the Narayaniya divide the Mahabharata into three equal parts.)

In any case, in the first chapter of the Narayaniya, Bhishma describes the birth of the sages Nara and Narayana:

I heard it from my sire that in the Krita age, O monarch, during the epoch of the Self-born Manu, the eternal Narayana, the Soul of the universe, took birth as the son of Dharma in a quadruple form, viz., as Nara, Narayana, Hari, and the Self-create Krishna. Amongst them all, Narayana and Nara underwent the severest austerities by repairing to the Himalayan retreat known by the name of Vadari, by riding on their golden cars.

My question is, what is the story of Nara and Narayana's brothers Hari and Krishna? The only other information the Narayaniya provides about them is Narada's statement that Hari and Krishna lived in Badrikashrama before Nara and Narayana:

That form took birth in four shapes for the expansion of the race of Dharma which have been reared by that deity. How wonderful it is that Dharma has thus been honoured by these four great deities viz., Nara, Narayana, and Hari and Krishna! In this spot Krishna and Hari dwelt formerly. The other two, however, viz., Nara and Narayana, are now dwelling here engaged in penances for the object of enhancing their merit.

The only other scriptural reference I could find to Hari and Krishna is in this excerpt from the Vamana Purana:

The divine body Dharma born from the heart of Brahma, had reproduced Hari, Krishna, Nara and Narayana sons by virtue of consummating with his wife Dakshayani.... Hari and Krishna engrossed themselves with exercise on Yoga. Nara and Narayana the greatest among all ancient sages began austerity with Parabrahma at the ever broad bank of the sacred Ganges in Badrikashrama, a place situated in the great Himalaya.

So first of all, how did Hari and Krishna's practicing of Yoga differ from their brothers Nara and Narayana's practicing of Tapasya? Second of all, what caused Hari and Krishna to leave Badrikashrama? Did they die or something? And in any case, what was Vishnu's purpose in incarnating as Hari and Krishna?

Are there any other Hindu scriptures which mention these two brothers? Note that this Hari is different from Vishnu's incarnation Hari who rescued Gajendra, whom I discuss here.

Answer 1

The Satsangijeevan (Ahmedabad edition) has vast chapters dedicated to this detail where Dharma (father of Nar Narayan) explains to Rishi Sanak the advent of Lord Nara Narayana.

Satsangijeevan (Adhyay 4 Chapter 31) "....The first Swarup of benevolent and merciful Lord will become known as Bhagwan Narayan, as He will redeem and grant salvation to innumerable souls that are lost in the never ending cycle of death and rebirth due to their ignorance or past deeds. He will also be known as Lord Narayan as human race can attain Moksha only through Him. He will also be known as Lord Narayan as He rests on a bed made of the coiled serpent Shesh in the middle of an ocean at the end of Atyantik Pralay. As He is the sole controller of uncountable universes, Maya and Kaal, His second Swarup will be known as Bhagwan Nar. In the absence of all feminine features such as a raised chest (or breasts) and long hair, He will be known as Lord Nar (the complete male). Bhagwan Nar and Narayan will proceed to Badrikaashram to undergo severe austerity together for the benevolence of people of Bharat Khand He will also be known as Lord Nar as He, through His potency, will guide the great kings on the path of righteousness.

The third Swarup of Bhagwan will be known as Lord Hari as He will remove all sorrows of the Devtas and anyone coming under His shelter.

The fourth Swarup will become known as Bhagwan Krishna as He will attract and merge within Him the brilliant radiance that has mesmerised and bewildered the Devtas and demons. O Muni! The other Devtas and I prepared for the worship of the four Swarups of Bhagwan after Brahma completed their introduction and naming..."

Satsagijeevan (Adhyay 4 Chapter 39) Dharmadev said, “O Sanak Muni! Our illusion and ignorance vanished after hearing Narayan Bhagwan’s sermon. Narayan Bhagwan asked Bhagwan Nar, Hari and Krishna to let the female deities worship them. Listening immediately to Lord Narayan, Bhagwan Nar said, ‘Hold on! Nar and Narayan cannot be separated. Nar always follow Narayan. Whatever Narayan does, Nar emulates.’ Just as Bhagwan Hari and Krishna were about to stop female deities offering their worship, Bhagwan Narayan asked them to relent. Understanding the latent desire of Bhagwan Narayan, Lord Hari and Krishna permitted deities to worship them. The female deities, aware of Lord Narayan’s wish, happily performed elaborate worship of Lord Hari and Krishna with camphor, Kumkum, sandalwood paste etc. They offered many expensive golden robes, ornaments such as bracelets and earrings and many flower garlands..."

Satsangijeevan (Adhyay 4 Chapter 40) Dharmadev said, “O Sanak Muni! Bhagwan Narayan got up to leave after soothing my mind with His divine sermon. He asked Brahma, Vishnu, Shiva and other Devtas to return to their respective abodes. He stopped Bhagwan Hari and Krishna from accompanying Him and for the benevolence of mankind, advised them individually.

‘O Hari! Please proceed to Vainkunth with Laxmiji. O Krishna! Please go and make Your home at Golok. O Vaasudev! Please proceed to Shwetdweep and O Sankarshan! You proceed to the bottom of earth to hold it steady. O Pradhyumna! Protect and sustain the whole universe by residing on Lokalok Mountain. O Aniruddha! Dwell as a soul of Virat and help in the process of creation.’ O Muni! Bhagwan Nar and Narayan, dressed as Naisthik Brahamcharis and ever eager to undergo severe austerities, departed for Badrikaashram after assigning the various benevolent tasks.

We were very depressed, but nonetheless, sprinkled flowers as a good portent on the path Bhagwan Nar and Narayan walked. Their radiant and round faces had a serene smile; their eyes were large and beautiful like petals of a lotus, their hands were long enough to reach their knees; their teeth were uniformly set and sparkling white, their large chest were adorned with the insignia of ‘Shree Vatsa’; their wide foreheads and beautiful ears lent their faces an extra splendour and their bodies emanated luminous radiance like the sun or moon. Holding Kamandalus in their hands, Bhagwan Nar and Narayan walked together, flanked by many people eager for their Darshan. I, other Devtas, Gandharva and sages led by Narad walked behind Him to bid Him farewell. Bhagwan Narayan stopped us after a while and asked us to turn back. He went to Badrikaashram and lived under a berry tree called ‘Vishala’ where Bhagwan Nar has remained in His service ever since. As others returned to their respective homes and hermits, I came here.”