Design Online Store with 3 Different Interfaces

The goal is to design an online store that sells fabric, wallpaper, and trimmings. We have 3 different website designs already finished, they will be registered at different domains, but essentially it is the same website with same items. We want these website to connect to the same shopping cart. The reason why we call it one site with three interfaces is because we understand that you will only have to write up the code once and then copy it on the other two sites. We also want it to connect to our internal system to pull up the prices and current stock. Some of the coding to keep in mind: these sites will have to have an option to be changed by us later - add new items, delete existent, as well as change banners, images, etc. Also, although websites serve the same purpose, they still are different from one another. For example, one has rotation banners on top, another has search by color on top. But it has all the same items, with same prices, pulling information from the same system. Please make sure you understand the task fully and ask any questions you have before bidding on the project. Thank you and we look forward to working with you.