That was a different baby! The one with the snake eye is Sigurd Snake in the Eye, lol. They're not following the legends exactly, but a lot of it is definitely in the story. Ivar the boneless should have been the eldest son (according to the Viking legends) and he wouldn't have been born deformed since he became a great warrior and king. The "boneless" part was probably something that was added once he was grown, just like Ragnar changing Bjorn's name after a battle.
SIGGY!!!! I knew Keamy was evil!
I don't understand why they're making supernatural shit seem real.
The Wanderer guy being able to take Ivar's pain away, and getting Aslaug to sleep with him, and making Ragnar's kids walk out onto the ice and Siggy sensing it somehow... I dunno, just seems a bit supernatural to me.