Hello and welcome to the 2nd Banana Theory! I want to make up for my original theory being wrong… so without further ado… Mr. Ree take it away!
Mr. Ree: Thanks Banana, a quick disclaimer! THIS THEORY CONTAINS CONTENT FROM ALL BOOKS BUT MITH! DO NOT read UNLESS YOUV’E READ TWATWK COMLETLY!!!
(I have no idea how to blur on a phone so don’t scroll down unless the spoiler warning does not apply to you…)
Ok, now we can get to the theory! Starting with the first book when Leeli sings with the sea dragons. At the end it says: Leeli felt something, Tink saw something, and Janner heard Yurgen speak. This also happens in N!obE when Leeli sings a song for nugget. However only JANNER can hear the sea dragons. Moving on to tWatWK, right before Gnag melds with Yurgen, Gnag had a full conversation with the old dragon… Gnag is the SECOND born, and as specified above, only the first born can talk to dragons. Personally I don’t think this is a plot hole. This is why: On Wingfeather Fandom it says that when a sibling dies the next youngest takes their place. All of Gnags siblings are dead which means that he has inherited the ability to talk to dragons! This would explain how Kalmer was able to get two dragons fully filled in on the situation, and ready to search for the first well, in the epilogue of tWatWK.
Mr. Banana: Thanks for unpacking that Mr. Ree! Putting all this information together it appears both Gnag and Kalmer inherited the ability to talk to dragons!
I don't think that it's necessarily true that one sibling takes the place of the other if one of them dies, except in regards to the Kingship. But I really like this theory, much more than assuming there is a plot hole! Maybe that IS how hearing the dragons works!