Yea so how is it canon lore?
Still no proof? Canon lore?... why? Media produced for the ride is just about as best a primary source for the ride's lore as one could wish for.
Obviously BGW didn't expressly set out to theme a ride to incest, but at some point along the way, wires were likely crossed creatively, the left hand didn't know what the right hand was doing, and the outcome is that the ride's main characters are both siblings and lovers.
Ultimately, it's just not that serious. It's just an amusing little factoid about BGW—no different than Fabio x Apollo, Sandra Bullock x Verbolten, etc.