It struck me when I was out fishing that there are several other surnames that ends with-ander like Erlander, Afander and Olander. So it is not mo that is the prefix but probably instead mol. Ander is a suffix/ending that means "man/human" from the Greek word for man, andros . But mol is not a common word today. It mean something like totally, fully or absolutely or a strengthening of an expression. So Molander would be something like "fully man/ true man". Still your ancestor and his brother might have taken that name because it started with mo, as in Motala.
Sorry for the many explanations but I hope my last one is clear :)