grammar - What is the possessive for several names?

If Alice and Bob each has a house, are these "Alice and Bob's houses" or "Alice's and Bob's houses"?

Does that change anything if each of the houses belongs to both of them?

Answer

"Alice and Bob's houses" implies that Alice and Bob jointly own more than one house. "Alice's and Bob's houses" could also imply the same thing. However, it would more commonly be taken to mean "Alice's house[s] and Bob's house[s]". To remove all ambiguity and still retain a similar form to what you now have, I would suggest "Alice's house and Bob's house".