“I don’t know that a mere “et al” is going to cut it with the Supremes.”
Have you ever seen a real SCOTUS petition as it’s filed with the Court ? They are a very peculiar, small size. There are several sections that precede the Petition’s arguments, including a thing called “Parties” where all the parties on both sides are set out fully.
That is, if the parties are not fully set out in the caption, in which case the parties section is either omitted or is repetitive as a precaution.