Json polymorphism implementation in c# project

WE NEED AN EXPERT IN JSON POLYMORPHISM. DO NOT APPLY IF YOU ARE NOT AN EXPERT. MENTION "VA PROJECT" IN YOUR REPLY TO BE CONSIDERED. ALL OTHER APPLICANTS WILL BE BLOCKED. READ ENTIRE POST BEFORE APPLYING. We have a C# WPF project and a c# WebAPi project with a shared C3 project of classes they both use. Prior to this, the classes were serialized and deserialized using XML. Several of the classes are derived from master classes and then extended. This worked well in xml, however in converting to the web API model, we are having JSON issues. We need a C# developer that can quickly add polymorphism to our JSON, and not add security holes. The XML looked like: <Root> <Entities> <Entity xsi:type="Entity_Individual" FirstName ="Joe" /> <Entity xsi:type="Entity_Business" Name="John's Company" /> <Entities> <Entity xsi:type="Entity_Employee" First_Name="Frank" /> </Entities> </Entities> </Root> Please ensure you know how to quickly implement the desired results prior to applying.