User blog comment:ChocolateSquirrel/Questions About the Dragons/@comment-49.150.40.228-20140919010808

1.) Yes it's weird, but, have you seen the Kyuubi? The Kyuubi has been sealed inside Naruto, same as Natsu. And whenver Naruto get inside in his body, there's this big prison. What do you expect? The kyububi is sealed inside his intestine? In the magic-related manga world, the Kyuubi is sealed in the chakra part of Naruto's body; maybe, Igneel is sealed in the magic factors of Natsu's body. And remember, Natsu's magic is fire, thus having volcanos. It represents Matsu's core magic.

2-3.) Grandeeney communicated through telepathy. She communicated Igneel and Porlyuscia through that power.

4.) When Acnologia came, that's when all of the Dragon Slayers to have this kind of sensation, not because of the Dragons sealed inside of them. Remeber that when Igneel telepathhicly talked to Natsu and went put of his body, he felt a burning sensation, different for the earleir sensation.

On the last question, just my theory