I know that well. But the brief is still wrong in claiming the defendants had to cross-appeal.
Why don’t you actually read the brief. That’s not what it says. It only says that the defendnnts did not present the issue because they failed to cross appeal. It then says, and cites authority to support that all appellate courts may examine standing on their own motion and indeed are obliged to do so. When you misrepresent what the brief says it’s fairly easy to find your own failure to read what it actually says wrong. Of course it is true that the appellate court may consider standing but you have inaccurately described the brief as saying what it does not in fact say. You have then assailed your own mischaracterization of what it says.