DMZ configuration question

I have a customer that shares an internal network with a completely different customer. Customer A and customer B are on 192.168.2.x network and both use the same application for their daily business. Customer B needs to setup a local web server for a separate application that only they use. Customer A does not want to open up their network to web traffic at all. Customer B is going to bring in a separate internet connection with a static IP for web server hosting. Customer B runs a database program that is going to run on the webserver. Customer B has to have constant access to the database/web server to input data. Any configuration recommendations for this scenario?

Thanks