shoulda got factory...Don't let your brother in law try to do it..ask the dealer where to go for it. check with inspection people.. they have a tester and can ticket you if its too dark....here in VA lots of peeps get it done in Tenn. and it fails here.
I live here in SD, and the limit is 35% on the front sides, 20% on the rear windows, and the windshield strip can't be below the AS-1 line. I think most states go about the 35% as I had a T-Bird done in Kansas once. I'd check with the local PD, or a pro shop should know the law on it.