It's hard to imagine the point of this story if neither of (A) Osborn regains control or (B) Osborn rejects the symbiote and then has to fight it happen. If (A), then he'd probably remake the symbiote into a goblin-y visage because he's, well, an obsessive nutball. If (B), then the Red Goblin suit may be his Carnage-fighting apparel.
The null case, where Norman is just the host and never regains control until Carnage is defeated, has potential for massive mayhem, but seems . . . wasteful. The other Osborns could still be imperiled (especially if that's how the symbiote cows Norman, e.g. it implies it'll jump to Stanley if Norman doesn't behave), but it's hard to see why Norman would need to be the host to put them in danger. It's also hard to see how the story where Norman is taken over by the symbiote for 4-5 issues and then is sad about the collateral damage is worth the build up we've gotten. Maybe if the Red Goblin is Harry fighting his father? I suppose I could see that (although it's a bit of a rehash of the American Son arc).
This is not to say that the Red Goblin won't be a resurrected Ned Leeds or Roderick Kingsley's screw up nephew, but I just don't see how that makes thematic sense or serves as any kind of capper on Slott's run.
As to the hypothetical and absurd Anna Maria clones, I'd bet on Grady from Horizon Labs as the creator - he seems like the type that would create his own girlfriend. You'd know which ones are clones because they're all wearing leis