my multi-vitamin has both, and I also take multi-b complex. they do not seem to affect my INR, and since I take the same dose every day, logically speaking, it seems that all would be same even if it did have effect.
Rest assured, Folic Acid and B12 will not affect your INR. It has nothing to do with warfarin's interaction with blood clotting. Only things that can affect INR are vitamin K foods and medications/herbs/etc that change the metabolism of warfarin.