Well...i'm gonna try my best to not confuse you. Megaman in this series was built by a man that was called the "Master" on a planet known as Elysium which was basically a robotic world that was clean of disease, no need for food or rest, and was all anti-war. Elysium itself seems to be the moon in the series. Now what gets alittle creepy is that it seems the planet Earth or Tera was created by Elysium somehow and the Carbons or well..all of Humanity was somehow based off of the Master's genetic code which is said I don't know how many fricken times...
But on Elysuim the planet of Reaverbots and such there were higherups as you probably heard of "Mother" or the "Mother Units" which were known as Yuna and Sera. Yuna was for humanity while Sera was against it. In the Master's dying days apperantly he created Megaman Volnutt to not only be his friend but a soul protector of his genetic code. Why he did this was because he knew Sera was one for wiping out humanity because they were weak and inferior to the life that was on Elysium. And on random night Megaman and the Master had flown down to Earth because the Master was hating the life on Elyisum, not being able to eat or sleep and do actual work in life.
Sadly, the Master began to die after he entrusted Megaman with the genetic code and told him not to let Sera get her hands on it or all of humanity would perish because of a special device with a specific program known as the Carbon-reinitalization program, to dumb it down...the apocolypse of all human life and restoring ruins and reaverbot life on Earth. Now I have an accurate guess but at somepoint after the Master's death, Sera and Megaman had a large scale fight that caused Megaman to lose his memory about all of Elysium and all that was once the Master. Now this may be unaccurate but because of Megaman's heavy damage from fighting Sera and managed to trap her in that device on Forbidden Island or whatever it was called, Mother Yuna must've somehow made it so Megaman appeared as a child/baby on Earth and left him at the doorstep of Barrel Casket.
Now with Roll's parents, her parents were famous diggers I assume and eventually as they were out on some kind of dig they crashed on the Forbidden Island and were never found.(They were presumed dead from there on.) Barrel had never told Roll of their fate because he never wanted to break her heart because she loved her parents so dearly.
Now a good portion of this i'm sure you completely already know but i'm just kinda using it as a refresher you could say and maybe filling in any blanks on some stuff you might have forgotten. But in the meantime I won't go into much more right now but feel free to post again or message me if you need more questions answered and i'll do the best I can to answer you.