(CEB|SHL Talent Measurement) Which one of following sentences is grammatically correct?
Natalie decided to invite the parents of her two brother-in-laws to her graduation party.
Natalie decided to invite the parents of her two brothers-in-law to her graduation party.
Natalie decided to invite the parents of her two brother-in-laws' to her graduation party.
Natalie decided to invite the parents of her two brothers-in-laws to her graduation party.
Natalie decided to invite the parents of her two brother-in-law's to her graduation party.