If the Approver list contians more than one approver then if any one of the approver will approve that request it should approved and then no need to approve other users those who are in the list. Automatically the request should be go into next stage.
If the approver list contians one user then the that user should approve, if any added in the next list then that user needs to be approve that.
Multi-level approver can be achieved by configuration.
Go to Custom Config :
Foundation --> Approval Process Configuration
Select Process Type --- Level
Change Management -- > Approval --> Approval Mappings
In this form you will have field's like
Approval For* -- Individual OR Group
Approval Indicator* --Service Request Definition, Service Request
Level* -- 0,1,2....
eg: Configure individual approval A, B, C for Level's 0,1,2 respectively.
--> When A approve's , it moves for B's approval and then for C's approval.
Hope this helps you.