I think it might depend on whether the "name" is actually a name or a title. Since Magnus has been shown to be a title (rather than a 'surname') in Animated, it would make more sense that its pluralisation could be irregular. On the other hand, Agatha is a Latin name that is still used today. It would be odd to refer to a room of people called Agatha as "a room of Agathae" rather than "a room of Agathas". So maybe it would depend on whether Optimus, Pax, Maximus and Primus are names or titles.