LOL! Nice selection. Although the FF isn't really a spoiler and the X-Men won't be a spoiler for many years!
I guess I should warn you the connection is a spoiler for 50+ year old plots!
I could remember "the real reason Batman's goofing off" on the first cover, so guessed what the connection would probably be. Checking plot summaries for the other two covers on GCD confirmed my guess. Congratulations on a very clever and subtle three-of-a-kind!