Hi
Our main expertise is Linux and its services, including all the three distributions that you mentioned, so installing and setting up Freeradius would be a piece of cake for us. We also have installed many different VPN services (soft-ether included) for our clients. We will set up Freeradius and Softether for you and configure the necessary settings in WHMCS plugin.
We’d be happy to hear from you, so we can start the job as soon as possible.