I think however you do it, it will either work or not, if pigs are going to get on they will do straight away, if not you'll know about it within half an hour. thats in my experience anyway. With my first attempt at bonding my 2 sows with my neutered boar i tried the 'neutral territory, gadual introduction' thing and it went wrong badly, everyone was just stressed out and they all kicked off. So when i got my other sow i just put her straight in the cage with my neutered boar, being honest i didnt even clean his cage out etc, they loved eachother straight away, it just worked! Then when i introduced a baby sow to another of my sows i just put them in the cage together, there was a bit of nipping for a couple of days but now they're best mates. thats the way i find best anyway, just leave them to sort it out as the woukd in the wild. They'll go on instincts and should accept eachother after a couple of days of sorting things out because it benefits them in the wild to be in a herd, in my opinion with sows if you keep taking them out they'll just have to keep re'sorting the pecking order if that makes sense? I'd try just leaving them together but if there's an injury i'd do it gradually. Thats just what i'd do though.