it probably depends on the host
human, idk--Edriss did seem to express a lot of shock and surprise that the human brain is bifurcated, so I think it's a reasonable plot element to include in a fic, or something, if that's what you're planning. One Yeerk driving the left side, and another Yeerk driving the right might make for an interesting psychological experiment.
as for other hosts, who knows? Hork-Bajir seem to have bigger cranial cavities than humans, and there was that one race (Ongachics, I want to say?) that had their brains distributed throughout their bodies in separate nerve clusters. I mean it is pretty explicitly stated that that means they're uninfestable, but maybe there could be some radical-thinking Yeerk scientist who tries to infest them with more than one, idk.
it's an interesting idea, and if you explore it in a fic, definitely post it here