I also agree that anything on Wikipedia should be taken with a grain of salt, which is why I said "rumored" and "IF it's true."
And I agree with the Alex and Maria idea! They should be depicted as cousins/best friends (though I prefer the former) who live right on the edge of Elwood City limits, and who are mainly friends with the Mighty Mountain/Glenbrook/etc. kids who live near them. That would explain why they are never shown hanging out with the Arthur gang. It's genius!