I'm pretty sure Freiderike is either Frederike or
Friederike. I lived in Germany and met several girls with both names. Mariechen is probably a nickname for
Marie or
Maria. -chen is something that makes a name cute and is usually attached to the full name, it sounds more affectionate. Kind of like -ita is attached in Spanish speaking countries.
Joschi may be short for
Joshua or Joscha.
The only one I like is
Marie (if that's the full name).