Moto,
Have you tried installing the double stand using the original bracket, or simply sandwiching it between the double stand mounts? I had the same issue on a Schwinn Jaguar. The double stand I have mounted in the same place and the original mount wasn't in the way.
I doubt seriously that removing the mount will compromise the frame integrity. I say this because I've found that the factory mount can be bent easily. In fact I welded in a new one on one bike because the original stand mount was twisting with the added weight of motorizing. The chain stays are welded to the BB and should hold. If you're concerned you could weld in a piece of flat stock where you intend to mount the double stand which would strengthen that area considerably. I did that and then used the piece I added for a exhaust pipe mount.
As for removing it...a hacksaw, a Dremal with a cut-off wheel, a side grinder with a cut-off disc... I wouldn't suggest simply twisting it until it breaks off. That's not a good idea.
Good luck.
Tom