You're right! I assumed they merged together...If, however, moving company A and company B led to the establishment of company C (and there are now three companies), don't use merge.
It's not very clear what the original means - I think we need more context on this one
I think "born" would be a better metaphor for a company that was split off from the original company or created by the original company while the original still exists. Your parents didn't cease to exist when you were born, did they?I'm writing about the history of Company C, which was born from the merging of company A and B.