Desarrollar software

Dear freelancers. The idea of ​​the project is simple. I have ERP phreebooks (PHP + MySQL application) and I want to get (SELECT), insert (INSERT) and update (UPDATE) from an application developed in C# Visual Studio .net (and Microsoft SQL). The idea is to avoid redundancy. Send and receive information from 1 single application (Useful for one area) and for another area to continue working on Phreebooks. The complication is to know the fields that are in use and that the information is transparent between departments. Attached image of the project idea, Best regards!