I’m not sure what it is you’re trying to accomplish with this setup. It sounds like you have an unRaid running a VM that is behind a reverse proxy connecting to another VM network for the client(s) to connect. To me, it is a bit over complicated.
But something to check out is the iptables. If you are using uncommon ports for the world servers, then those also need to be opened in MineOS. Make sure that the proxy allows the content to pass, as well.
If all those systems are necessary, then you may need to look into setting up a VPN… (Not sure how to go about that, myself.)