Yes you can assign multiple users to forms.
From the xCenta Dashboard, click on Tools > Admin in the top right of the screen.
From the administration screen, click on Manage Site Indexes and Forms.
A new screen will appear listing the indexes that are available. Select the index you wish to open by clicking on the index name.
To add users to a form you first click on the 
icon on the form you wish to add the users to.
A new window will appear. Click on Add User in the drop down box. Select the user(s) you wish to add from the list provided. You have to add one user at a time. Then click OK to confirm.
If you are unable to follow these instructions, you may not have the required user permissions. Please contact your Site Administrator.