Well, I have Viola Odoratas too, and they seem to grow equally well in sun or shade. Too much hot sun may make them droop however, I just water them to make them perk back up.

I'm new to violets but I bought some Birds Foot violet (viola pedata) this year and was told to plant it in full sun in dry, sandy, rocky soil. I planted them in a raised bed filled with sand, pebbles and some soft soil. So far they are doing ok.

Good advice from Trisha for V. pedata.

For the others, full sun would do for them all, to generalize. But if you can, I would advise aiming for somewhere with at least a little shade and humidity, not least to reduce the chances of red spider mite in a long hot summer.
More specifically, the violets in your list (as opposed to the pansy types) can be planted under deciduous shrubs in full sun - so that they get all the light going in spring (when they flower), but get the shade during summer (they can take quite a lot then).

Thanks!