I believe this is documented in Drupal's Form API Reference.

You should be able to set the labels corresponding to each checkbox in the #options array. The array can be of the format:

array(
  'submitted_value1' => t('Label 1'),
  'submitted_value2' => t('Label 2'),
);

Each key of the array is the value that will be submitted when the form is submitted. The value of each element in the array is what is displayed.

I believe this is documented in Drupal's Form API Reference.

Format a set of checkboxes. #options is an associative array, where the key is the #return_value of the checkbox and the value is displayed.

You should be able to set the labels corresponding to each checkbox in the #options array. The array can be of the format:

array(
  'submitted_value1' => t('Label 1'),
  'submitted_value2' => t('Label 2'),
);