Yea... In my school everyone takes up calculus ! XD but I'm not living in Japan and yes. You have to have a certain amount of brain power to be good at calculus... XD though we have a cheat formula here to understand calculus XD
Gin --> Shinichi's cousing
Kaito Kuroba --> Shinichi's another cousin
Anokata ---> Shinichi's grandparent.
Mouri Kogoro ---> Anokata's adopted son who is being begged to take in Shinichi and trains him to be the ultimate weapon!
O__O