Today's opinion from the California Supreme Court sounds exactly like what I would say to one of my first-year law students who was confused about res judicata.
Justice Corrigan's opinion is careful, patient and slow. She essentially says: "Look, I understand that this stuff is confusing. The terms are in Latin, and sometimes even smart people (e.g., us) use the phrase 'res judicata' to describe two different things. So I can understand why you might well find this difficult. But you're allowed to sue two different parties in two different lawsuits. The second suit isn't barred by what's properly called 'claim preclusion'. Even if there's joint and several liability. Even if you could potentially sue them both in a single lawsuit. It's just not required. Your call whether you want to file one lawsuit or two."
There's a reason today's opinion is unanimous. Because that's clearly a correct statement of the law.
Even if the trial court, and the Court of Appeal, below got it wrong. Like many, many law students before them.