How should I re-introduce my guinea pigs?

[JennyCat! :3]

My guinea pig (Cocoa) was neutered a few weeks ago (about 4 or 5?). Since then, him and the female (Izzy) have been seperated.
I had problems at first, because they would make so many noises that I couldn't even sleep at night. But once I put their separate cages to where they could see each other, they calmed down.
I've tried to put them together a few times since then, but the Cocoa chases Izzy around and tries to mount her. Izzy gets p*ssed at him because of it, and tries to fight him. They weren't like this before.
Also, I'm pretty sure the female is ALREADY pregnant. The vet said she isn't, but I still kind of think she is. So I don't want him putting stress on her if she is pregnant.

I don't really know how to re-introduce them. Cocoa is healed up enough now to be back with Izzy, but I don't want them to hurt each other. How should I re-introduce them?

 

[Dizzie]

Set up a neutral area, that smells like neither of them and let them play there daily. Put their cages next to eachother so they can see and smell eachother when they want and once they stop chasing and such start putting them in teh same cage for a few hours a day. The humping thing is also a dominant thing, reintroducing them means they have to decide who is the head pig so your going to have to let them duke it out a bit just let them do it while your there to monitor them.