Final answer:
Separate legal advice for each client is NOT a requirement for joint retainers. A joint retainer fundamentally requires a common interest, consent from all parties, and confidentiality between clients.
Step-by-step explanation:
When it comes to the requirements for joint retainers, the option that is NOT a requirement for joint retainers is 'Separate legal advice for each client.' While clients may choose to seek separate advice, it is not a necessity for the formation of a joint retainer agreement. The foundation of a joint retainer is built on the three pivotal aspects of having a common interest in the matter, obtaining consent from all parties involved, and ensuring confidentiality between the clients. A joint retainer must align with the right to an attorney as articulated in cases such as Glasser v. United States, which highlighted the conflict of interest that may arise from simultaneous representation and its potential violation of the Assistance of Counsel Clause of the Sixth Amendment.