Question About Phineas And Ferb Summer Belongs To You? Doesnt Make Sense. (Isabellas Nationality?)?

Okay this doesnt really have anything to do about the episode "Summer Belongs To You" Well actually it does. So It Says Isabella's Full name is Isabella Garcia-Shapiro? And clearly i mean thats a spanish name right? But in the summer belongs to you episode they stop in tokyo, and visit staceys and isabellas cousins? not that spanish people cant live in tokyo but they looked really you know...japanese and they were speaking it... and i mean i know its just a cartoon but if there spanish how are they japanese? O_o Just something that doesnt make sense. Even Though its a cartoon. :\ Are Stacey and Isabella sisters right?