1. UIToggle.GetActiveToggle(1) gives you the active toggle from the first group of toggles. If you know which group you're working with, that's a fine way of retrieving the active choice.
2. Don't try to set anything to 'false'. In a group of toggles, only one toggle can have a 'true' state, so setting one toggle to 'true' will automatically turn off others. If you want to turn off all of them, then setting their 'value' to false is enough, but you will want to also set the "optionCanBeNone" to 'true' first, otherwise it won't be possible to turn off the last option.
3. See #2.