My brothers-in-law's (not: brothers-in-laws' or brothers'-in-laws') firm sank financially. The pl. possessive of brothers-in-law is brothers-in-law's, correct?
What about the pl. possessive of attorney generals?
Would it be:
Pl. Possessive
The attorney generals' firm sank financially. (more than one attorney general)
The attorneys general's firm sank financially. (more than one attorney general)