When you import questions in GIFT / AIKEN format, there is no option to switch on / off the shuffling of the answer choices. So, no need to change your import formats.
 The shuffling of answer choices within each question can be selected /
deselected from the Quiz > Gear icon > Edit settings > Question behavior > Shuffle within questions yes/no
 The shuffling of questions across the quiz can be selected / deselected from the Quiz > Gear icon > Edit quiz
> 'shuffle' checkbox
The choice numbers (or letters) can be hidden via CSS
Just add the CSS
below to the Raw SCSS of the theme.