There are two document options when using grouped checkboxes with the API.
Template workflows
When using Dropbox Sign templates, you can group checkboxes directly in the template editor. The links below show the sign.dropbox.com editor, however, the process is the same when using the embedded iFrame editor.
Dropbox Sign Templates
How do I create a template?
Grouped checkboxes
Document workflows
When sending documents out to sign, grouped checkboxes can be used with text tags.
Text tags
Section "Grouping Checkboxes"
Section "Checkbox field grouping"
Checkbox field grouping
Checkbox field groups accept an optional validation rule, which must be met before the user can submit the signed document. These are the options you can specify for validation rule.