So we finally know what happened to Igneel, Metalicana, and Grandine!! :D Yes, they were inside the dragonslayers all along. I'm pretty happy about this (mostly since I've been speculating about it ever since the Fighting Festival Arc), but there are a few questions I have about all this:
•Pretty much every time we've seen Igneel, he's been in some volcanic area. So there's a bunch of volcanoes inside Natsu? (or something like that, anyway)
•There was that one time when Igneel and Grandine were talking about how Natsu and Wendy were going to meet soon, but how did they communicate at all if they were inside their dragonslayers?
•Porlyusica said that Grandine told her about Sky Drill and Milky Way, but again, how did Grandine talk to her? (Although, that could have been before July 7 X777.)
•Sting and Rogue were also reacting to Acnologia the same way the other DS were, so does that mean they never actually killed Weisslogia and Skiadrum?
There's quite a few plot holes surrounding this at the moment (hopefully they get cleared up). Go ahead and speculate all you want.