First, what does this opposition want?
Marg bar dictator. It's pretty clear on the vids, maybe try using headphones if you can't hear it. Could be time for a hearing aid.
Second, who leads it?
You'll find out when it's safe for them to reveal themselves.
Third, through what process will this opposition displace the government in Tehran?
Wait and see. They're the experts.
[These questions were also answered in great detail by other people but I feel short answers are more suited to people of the Leveretts' mental caliber.]