Once the user creates a ticket that is assigned to have an approval process with it must get assigned to a tech, that tech does not have to be the approver. The approver either needs to use the email that you show or log into the CLIENT side of the interface to see their approvals. If the approver is a tech you need to ensure the client login is setup in their profile and that they know to click the small person in the upper right corner of the screen the jump between the sides.
There is an existing enhancement request to enable techs that are also approvers to see those from the tech side (Ticket Approval from Technician Interface )
There is currently not a way to disable, or change the buttons. Please see this existing enhancement request (Ability to disable NO button on a per approval process basis)