You did not specify a jurisdiction, so this answer looks at the Berne Convention and the United States.
To summarize, you are correct about joint works; the "death of the author" is taken to be the death of the last surviving author. The general approach for works with corporate authorship is to specify a fixed term that takes into account both the date of creation and the date of publication, if there is one.
Here's what the Berne Convention has to say in Article 7bis:
The provisions of the preceding Article shall also apply in the case of a work of joint authorship, provided that the terms measured from the death of the author shall be calculated from the death of the last surviving author.
This is pretty clear; your presumption is correct.
In article 7, there is special consideration for cinematographic works:
(2) However, in the case of cinematographic works, the countries of the Union may provide that the term of protection shall expire fifty years after the work has been made available to the public with the consent of the author, or, failing such an event within fifty years from the making of such a work, fifty years after the making.
That is, the copyright term is fixed at fifty years from the date of creation, but if the work is published within that fifty-year term, then the copyright term extends until fifty years after the date of publication. That's the 1971 text; I suppose the specific duration may have been adjusted in the meanwhile.
The United States Code, at 17 USC 302, has similar provisions about copyright term in joint works:
(b) Joint Works.—
In the case of a joint work prepared by two or more authors who did not work for hire, the copyright endures for a term consisting of the life of the last surviving author and 70 years after such last surviving author’s death.
In a "work made for hire," the copyright is owned by the employer; this would cover movies and other cases in which the creation is attributed to a corporation rather than an individual. These cases are covered by the next paragraph:
(c) Anonymous Works, Pseudonymous Works, and Works Made for Hire.—
In the case of an anonymous work, a pseudonymous work, or a work made for hire, the copyright endures for a term of 95 years from the year of its first publication, or a term of 120 years from the year of its creation, whichever expires first. [...]
The deleted text concerns anonymous and pseudonymous works.
