Hi,
Here in Canada (well at least in my province) the household voltage is 120/240 volts. The 120 volts is for lights, TV, small appliances, etc. The 240 volts, when electric energy is used for those, is for water heater, kitchen stove, cloths dryer, electric heating and other heavy appliances.
The breaker box is fed by 3 wires: black, red and white, plus a bare ground wire. Black and red gives 240 volts, black and white 120 volts and red and white another 120 volts.
Now, I am not aware that a 120 volts only breakers box is available. So you will probably need 2 spaces on on your main box (because 240 volts need a double breaker) for each secondary box you want to feed, a total of 4 in your case.
Would it be legal? I don't know. It would probably depent on what kind of installation you have actually.