Conduct usability testing on WordPress website for charities and provide feedback

We are developing a WordPress website which is designed as a free service for charities to use. We help charities build on their services through a peer-to-peer advice service, an expert knowledge base, and the option of referring more complex questions to partners. We need someone who has knowledge of how charities operate to review our website acting as a person representing a charity, a person representing volunteers, a person representing a partner, a person in general wanting to know what we do - and tell us how we can improve our website. For example: is our registration process user-friendly? is our website design good? Is it easy to understand what we do? Are there any errors on our website? Is it easy to use the peer-to-peer advice service? We need to get suggestions via e-mail to our developer and test manager. We might also have a bug tracking tool to track bugs. It will be great if the person also has knowledge of how WordPress operates so we can get not only the error but a suggestion of how to make it better.