Show Duplicate Leads while Conversion

We have a requirement that when user clicks on convert button on lead , we should show a pop up listing all duplicate leads(leads with same company/Dealership). AT that time what ever leads rep select, those should also be convered into opportunity.

that means all the duplicate leads along with master one should be converted into single Account ,opportunity.

Can anybody please guide me with the solution. Let me know if you need further details.