When is it appropriate to use "was" (or the singular form of a verb) when two subjects are grouped? Would the usage of the singular imply the subject is "the relationship of those two subjects"
E.g. Key and Peele was/were funny. (An established group)
E.g. Jim and Pam was/were the best part of The Office. (a specific pairing often used together)
E.g. Chewbecca and the Porgs was/were entertaining in The Last Jedi. (In this case does was have a different meaning than were?)
E.g. Jack and Jill was/were running.
My "intuition" is that was is appropriate in the first three cases, while it's obviously not appropriate in the last one, but I can't determine why it would be appropriate in the middle two.