Will you connect locally or over the internet?
When you start the VNC server, the port will already be different in each of the places. For a local connection, it will be enough to specify IP:Port or IP:N, where N is the display number (0 is for the first place).
To access from the Internet, you will need to set up port forwarding on the router, and you may need to assign an IP for workplaces.

Can I set up two separate instances ofslope Ultra VNC, each with its own port?

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Yes, you can run multiple instances of UltraVNC on different ports. You’ll need to create separate configurations for each instance and specify unique ports in the settings. Running them as services might make management easier (visit here). Give it a try and see if it works for your setup!