I would have thought that someone like you who is very concerned about security, would know that an https service on an RFC1918 address is always going to give dire tla certificate errors.
I just want two separate networks. The WNetwork1 network should be restricted by DHCP so that only one device can connect. From WNetwork2, I want to access that isolated device so that no one but me from network, just only from access 2. network can access it. Why is this a bad solution? Or how would you solve this?
No, it is the https protocol that will fail. Https is designed to prevent redirection/port forwarding as well as the use of RFC1918 addresses for security reasons.
You need to be certain the web site you are accessing is the secure site you thought it was.