I'm not familiar with Viscosity and its abilities but it sounds like only your Mac is connecting to the VPN and not other devices?
If this is correct, you best option is to get your router to connect to the VPN and therefore everything that connects to your network is through the VPN. The way I did it is by flashing my router with software called DDWRT. It's fairly complicated, took me some hours, but worth it as it's only a one off thing then all your devices will connect to the VPN.
I see what you are trying to do with enabling internet sharing...but I don't think its a very efficient way of doing this.