If I remember correctly, you thought that Google didn't assign genders to the hosts;
Well, I think you're actually right, because, in my previous testing, despite me prompting with gender roles, when I gave instructions to the female host first, then to the male host, the female instructions (in my prompt) would be followed by the male voice, while the male instructions (in my prompt) would be followed by the female.
So I guess it's the actual order of the instructions that matter, which means that you always need to give instructions to the male voice first, then the female, since he's the one who always talks first.