This episode of Sunda and Upasunda is given in Mahabharta Adi Parva wherein Janemejaya questions Vaisampayana as follows
How did pandava's wife Draupadi obey all of them?
How is that no disputes arose amongst those illustrious rulers of men (pandavas), all attached to one wife (draupadi)?
To this Vaisampayana says, Once Sage Narada visted the pandavas and addressed the pandavas to establish a rule among themselves, so that no disputes may arise amongst the pandavas on account of Draupadi.
Sage Narada Says:
There were, in former days, celebrated throughout the three worlds, two brothers named Sunda and Upasunda living together and incapable of being slain by anybody unless each slew the other. They ruled the same kingdom, lived in the same house, slept on the same bed, sat on the same seat, and ate from the same dish. And yet they killed each for the sake of Tilottama. Therefore, O Yudhishthira, preserve your friendship for one another and do that which may not produce disunion amongst you.'the similar question was asked by, Yudhishthira to Sage Narada.
Then Narada goes on to describe the story of Sunda and Upasunda:
Hearing these words of Yudhishthira, Narada replied, 'O son of Pritha, listen with thy brothers to me as I recite this old story, O Yudhishthira, exactly as everything happened. In olden days, a mighty Daitya named Nikumbha, endued with great energy and strength was born in the race of the great Asura, Hiranyakasipu. Unto this Nikumbha, were born two sons called Sunda and Upasunda. Both of them were mighty Asuras endued with great energy and terrible prowess. The brothers were both fierce and possessed of wicked hearts. And those Daityas were both of the same resolution, and ever engaged in achieving the same tasks and ends. They were ever sharers with each other in happiness as well as in woe. Each speaking and doing what was agreeable to the other, the brothers never were unless they were together, and never went anywhere unless together. Of exactly the same disposition and habits, they seemed to be one individual divided into two parts. Endued with great energy and ever of the same resolution in everything they undertook, the brothers gradually grew up. Always entertaining the same purpose, desirous of subjugating the three worlds, the brothers, after due initiation, went to the mountains of Vindhya. And severe were the ascetic penances they performed there.
Lord brahma , ever seeking the welfare of all, came unto those great Asuras and asked them to solicit the boon they desired. Then the brothers Sunda and Upasunda, both of great prowess, beholding the Grandsire, rose from their seats and waited with joined palms. And the brothers both said unto the God, 'O Grandsire, if thou hast been pleased with these our ascetic austerities, and art, O lord, propitious unto us, then let us have knowledge of all weapons and of all powers of illusion. Let us be endued with great strength, and let us be able to assume any form at will. And last of all, let us also be immortal.' Hearing these words of theirs, Brahman said, 'Except the immortality you ask for, you shall be given all that you desire. Solicit you some form of death by which you may still be equal unto the immortals. And since you have undergone these severe ascetic austerities from desire of sovereignty alone I cannot confer on you the boon of immortality. You have performed your ascetic penances even for the subjugation of the three worlds. It is for this, O mighty Daityas, that I cannot grant you what you desire.'
Sage Narada continued :
'Hearing these words of Brahman, Sunda and Upasunda said, 'O Grandsire, let us have no fear then from any created thing, mobile or immobile, in the three worlds, except only from each other!' The Grandsire then said, 'I grant you what you have asked for, even this your desire'. And granting them this boon, the Grandsire made them desist from their asceticism, and returned to his own region. Then the brothers, those mighty Daityas, having received those several boons became incapable of being slain by anybody in the universe.
These two daityas, Sunda and Upasunda fought against each other on account of Apsara Tillotama, who was created by Lord brahma, so that the two asura brothers will fight each other to death in order to possess tillotama. For more details please refer to this link.
Coming to Mareecha and Subahu, the following is description given in Wikipedia:
Maricha was the son of the demon Sunda (son of Jamba or Jharjha) and Yaksha female Tataka. Tataka was daughter of the yaksha king Suketu, who had gained her as a blessing from Brahma. Maricha also had a younger brother Subahu. The siblings were very handsome and noble in character. They became skilled in sorcery. Once, Sunda attacked the ashram (hermitage) of the sage Agastya in an intoxicated state. The angry Agastya burnt him by his meditative powers. When Tataka came to know of Sunda's death, she and her sons attacked Agastya to wreak vengeance on the sage. The sage cursed Tataka, Maricha and Subahu, transforming them into wicked, hideous, demonic rakshasas. Tataka and her sons then went to Patala (underworld) to seek aid from Sumali, the patriarch of the rakshasas. Sumali took them to his grandson, Ravana, the rakshasa king of Lanka. Ravana helped the trio capture the states of Malada and Karusha, situated on the banks of the river Sarayu near its confluence with the Ganges. The trio destroyed the states and turned them into a dense forest, which became known as the forest of Tataka. They terrorized the people, devouring anyone who dared to venture in that forest. The gods, demons and men, as well as even the sun and the clouds did not dare to enter the territory of Tataka and her sons.
