Second Approver for Invoices Related to Purchase Orders

Is it possible to please have a second approver for invoices related to Purchase Orders? This would be similar to the way a PO can have a second approver. 

Approval MUST take place before the invoice is authorised and sent to Xero. So you would have a 'submit for approval' button for the invoice raiser and a 'approve/authorise' button for the approver. 

Dear/Cin7 works really well by sending the invoice straight to Xero as an awaiting payment, but our process requires a second check to catch any issues before it reaches 'awaiting payment'. It would be great if this check could be done in Dear/Cin7. 

Can we also have the ability to trigger an email to a particular email group when an invoice is created? E.g. it can still be in draft status and the email group would be able to receive an email saying a new invoice needs to be authorised.