Maybe Edina is ESFP? I think she's definately FP, and more E than Patsy. I think Patsy is more I.
I think Saffy is INFJ because she is definately an introvert (has a nerdy friend Sarah, studies a lot). INFJs are often cited as having amongst the highest GPAs. INFJs are considered bookworms. She has a moral conscience because she often exclaims the name of one of her family members in order to shame them, eg. "Gran!" or "Mum!". She is quite bashful when it comes to romance, and I've read that INFJs are amongst the types most prone to social anxiety. She's kind of like the responsible, mature protector of her mother.
There's not many appearances of Sarah throughout the series, but I think she's probably an I since she's a university student who is nerdy and has study sessions with Saffy in Saffy's home. She's not much of a party animal because she exclaimed that she "almost drank a whole can" of beer like it was some amazing feat that she's never done before. I think an E would be less likely to say that.