How can I remove internal padding on a RadioListTile so I can use 3 RadioListTiles in a row?

You can use Radio + text widget instead of RadioListTile. For removing internal padding in Radio widget set:

                  Radio(
                    visualDensity: const VisualDensity(
                        horizontal: VisualDensity.minimumDensity,
                        vertical: VisualDensity.minimumDensity),
                    materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
                    .....
                  ),