You will have to punch them on one side and file the protruding head on the other side. Then, punch them from the filed side and file the other side. Back and forth, until the flared heads are totally removed. The pins should go a little further each time.
I must caution you that you will probably ruin the knife during disassembly. Even if you don't, you probably will during reassembly.
Can you not find the same knife in a single blade version?