Robert C. answered 03/24/19
Master's graduate with experience editing technical writing
You should always refer to the two authors together, so your example is nearly correct. The in-text citation (for MLA) would be: "Boats need water to float" (Duck and Mouse 101). Provided 101 is the page number.
You are also correct that, in most cases, you will want to refer to the author and not the book. So you could say: In Boats are Fun, Duck and Mouse argue that water is necessary for a boat to float (101). These rules apply to sources with known authors. There are times when you would refer directly to the source rather than an author, for example, when quoting a definition from the OED you would use a different set of rules for both the in-text citation and the Works Cited entry.