Hold sellers responsible for botched window installation?

[Eric T.]

Here's the situation. Purchased a house last July and the inspection revealed several windows were rotten. Sellers agreed to fix, but the sizes are custom. Sellers arranged through Pella (and an independent contractor affiliated with the local Pella) to install. They paid for windows upfront and then money was held in escrow for the installation + extra which has not been released. Well, the installation has been totally fubar. I don't want the contractor back at this point - they keep botching things up. Talking to a RE attorney next week and getting an inspector out this week, but I'd like some real world advice from the experts here. Thanks!