Please help!!! Brand new Tires become bold in 3 months

Hello,
I own 2005 Nissan Altima 3.5SE that has Front Active Tuning Koni Suspension and the rear is custom made "Two Regular Nissan Shocks welded together on both sides (see pic. attached). Three months ago i ordered a new set of tires for the rear because the tread got weared out pretty fast for some reason. So i got everething installed and balanced and the wheel alignment has been done at the local shop in Feasterville, PA.
The problem is that after 3 months the handling become very bad, tons of body roll and not agressive at all!!! So i thought my rear suspension is dead! So, i order a new susopension for the rear and when i was about to install it, i noticed this: (look at the photos attached, its both right and left) The rear tires are almost naked! On the edges! I asked the guy who did the alignment what happened? And he checked the car and he said that he doenst know, everething seemed fine! (he owns a local shop and he has pretty good equipment i would say)
So, i ordered the set of tires that i will replace on the rear. But i need to know what could cause such a problem? Is it because the guy doesn't how to do the alignment? Same thing happened last time to me.... Or maybe its the suspension set up? but what i think, is that when he does the alignment he enteres the stock information of 2005 3.5SE Altima that has 17" tires and mine are 18"??? and something gets mixed up!
Guys! I need your help really fast , because those tires will go bad on me anytime soon!
Thank you!
http://www.deliciouspizzeria.com/rear.jpg
http://www.deliciouspizzeria.com/tire_1.jpg
http://www.deliciouspizzeria.com/tire_2.jpg
http://www.deliciouspizzeria.com/tire_3.jpg
http://www.deliciouspizzeria.com/tire_4.jpg
http://www.deliciouspizzeria.com/tire_5.jpg
http://www.deliciouspizzeria.com/tire_6.jpg
http://www.deliciouspizzeria.com/wip2.jpg
http://www.deliciouspizzeria.com/wip3.jpg

I think your camber is off and therefor eating your tires up like crazy. Looks like your car is also lower, could also be that you are rubbing.

You have a classic case of negative camber. This is the angle between the vertical axis of the wheel and the vertical axis of the vehicle when you look at the car from the front or rear more the half the bottom would be away from the car. This causes the inside of each tire to wear at a much greater rate then the rest of the tread. Suspension alterations can change the geometry of the suspesion, hence alter the alignment. You will keep chewing up tires until your get the alignment right.

Alignment, camber, and toe. When you go get that fixed I think you will see a big difference.