I agree and disagree with some of them, my choices would the following.
Taeyeon: Vocal, specifically vocal because she can show how it's really done. Music is too much and tae doesn't really know much instruments.
Sooyoung: Japanese, I agree because she knows the most and she can be really witty. I would love to learn japanese form her.
Yuri: Morality is not something that can't be taught, to me it has to experience. Besides there isn't really a course like that, perhaps the closest thing would be sociology. But I would perfer her to the P.E teacher because really she knows how to swim and her pitch in the baseball game. WOW. And the fact that she is a health nut, could also help.
Sunny: I agree with the family ed, because of the SUJU H video. She can be really charming in that class.
Hyoyeon: I see her more as the cooking/ family ed teacher. Because she can cook really well first off, and she is very frank. I think she suits the job more. But the P.E teacher seems like also a good choice maybe she can pair up with Yuri?
Tiffany: Although blowing up the chem lab may seem fun, it is not and I would rather not have her blow up things because really that shows she doesn't know much. Tiffany would be better off as a Kindergarten teacher because she can really hit it off with the kids.
Jessica: When she speaks english it is to die for! And also because she reads tons of books so that would make her a better choice for the job.
Yoona: Drama would be her strong suit, with her being on acting shows already she also her training herself. Makes her the prime candiate.
Seohyun I would see her more as the music teacher beacause she knows piano, the music notes, and all that other stuff really well. She's patient and she seems to know a large range of songs too.
★彡Someone else must be wishing on my star...
"Baby, because I was just an afterthought"