Collaborators and Approvals

Hello all! 

Just a quick question. I have 50 collaborator accounts. Lets say 1 collaborator and 1 full user is assigned to the task. The full user sends a task approval to the collaborator. The collaborator approves it but then they want to check it with another collaborator account that is not linked to the task. They create an approval but the other collaborators in the account do not appear. Only full users.  How can I make them appear - is it a setting? I'd like to push the ownership on to the collaborator. 

Cheers!