With great difficulty.10/10 for the sheer awesomeness factor. Bravo.
[Random] I wonder how O&M would work in the sonic World, though... [/Random]
Sonic = Millie (The hyperactivity kinda translates to speed. Plus she is relatively carefree)
Tails = Depending on if you go with the 'adorable tag-a-long' angle, or the 'smart and nice' angle, either Timulty or Stephan. Though neither is a perfect comparison.
Knuckles = ...Avery, I think. Since he's the closest thing to a non-bully to have any sort of attitude that even approximates 'cool'. Plus he's stupid enough to be tricked several hundred times by the same person with similar ploys.
Eggman = Felicia, if we have Millie cast as Sonic... Except, not, due to the next section. So I guess either Jeramy on the whole bully factor, or Stephan on the desiring power of some description factor.
...The extended family... This is why it's awkward, I don't think there are enough characters in O&M to fill all the rolls.
Amy = ...Closest to anything like the equivilent role in O&M, assuming the base premise of Millie as Sonic which is the only one I'm fully happy with, would probably be Avery, due to the whole Story of Chaulk. Which is a doublecasting.)
Big = I cannot come up with even a stretched analogy here.
(Which I guess would make Froggy = And the same here. Though, possably Timulty again for Froggy...)
Shadow = ...If you assume that Shadow was meant to be Sonic's morriarti figure (equal and opposite) then that would... Make Felecia Shadow rather than Eggman.
MEHTUL Sonic = ...How many morriarti figures does Sonic need, anyway? Another character who's most natural casting would be Fellicia due to the casting of Millie as Sonic.
Rouge = Extremely worryingly, the closest thing to a natural casting in this role would be Isolde, I think. Which is a huge stretch of "Well, conspiracy weilding is a little like spying". Oh, well, there is Stephan's or Avery's wanting to get rich that could make them less stretched casts.
Cream = Ozy (uhh... Polite and helpful) Or Timulty (cute and innocent. Unfortunately...)
(Cheese kinda makes a natural Timulty. Possably.)
These were not written in the order they're presented, so references to one another might not be in the order you read them.
um interesting...