yea somethings odd.

The offest will be engraved on the back of the wheels, or on a sticker covered by brake dust. not hard to find.

And yes a lower profile tyre will help, a semi slick tyre will be bigger then a street tyre in the same size, if it turns out the wheel are ok, get a lower tyre to stretch under the guard.
Some camber would help too but try finding out what the problem is first.
are you sure the wheels arent staggered widths? maybe even same width but different offsets?
trust me its all possible.

btw, does the car drive fine/straight/no vibrations?