The way I'll have it set up is that the three Wiis (and the Wii U) will all go to the main TV. Then, optionally, one of each of the other two Wiis will each go to a smaller TV as well (Any Wii on the big TV, or a different Wii on each TV).
This, of course, will generally mean that I'll have the big TV on at any point - but if I'm playing a game that requires the sensor bar, it'd be awkward on the smaller TVs. But, the only time I can see requiring one of them on the small TV would be for something like Brawl or Mario Kart - online games that don't really use the sensor bar.