Users can not approve any of the other approvals even if they are belong to the same user group.
This is expected behavior with the approval records when users attempt to approve any other user approvals. The constraints are set on the OOB ACL (sys_ID=476967a60a0a0b0c0019e98fbc0a83d8) on the [sysapproval_approver] table, and on the 'Approve' UI Action (sys_ID=846762e1c611227d00d8f3173b5d29db) conditions.
The 'Approve' UI Action (sys_ID=846762e1c611227d00d8f3173b5d29db) which you see when you select all the approval records has the condition:
current.state == 'requested' && isApprovalMine(current)
This means the UI Action is available only on the user's own approvals.
The ACL (sys_ID=476967a60a0a0b0c0019e98fbc0a83d8) on the other hand will only allow users with 'admin' role to approve, or if the approval is their own.
In order to modify the behavior, remove the second condition from the UI Action 'isApprovalMine(current)', and add 'catalog' and 'itil' roles to the above ACL. This will allow any user from the group to go ahead and Approve all the records in one go.