This question already has an answer here:
Which is correct: [Bonus question: should there be a question mark here instead of a colon?]
The book contains Marx and Engels' theories about the nature of society and politics.
The book contains Marx's and Engels' theories about the nature of society and politics
It seems to me that the former is more common, but I am confused here since the latter seems more logical to me (and matches what you would see in my native language Icelandic).