How do I create a collaborative webform using Webforms?
I have been able to share a single submission with a role. 

First, enable the 'save draft' option in webform Advanced Settings The 'Save Draft' option is here: webform/configure -> Advanced Settings -> Show "Save draft" button

Then, create a role with 


'Access all webform results'
'Edit all webform submissions' 


permissions. Any user assigned to this role can edit a submission started by another user.

The edit submission link (node/%/submission/%/edit) will be shared with the appropriate team members.