Publish or subscribe to another roscore/master

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If I not mistaken, only one roscore/ master can be present. Try ROS SSH to transmit messages from one PC/ controller to another.

ROS 1 is designed to run with a single roscore. You can play various games to make nodes from one roscore talk to another roscore but I wouldn't recommend it, since that can go off the rails quickly.

To exchange data between nodes from different roscore instances, I would suggest using "something else" as the bridge. I would first suggest trying ROS 2 as the "something else" bridge protocol, but you could also try any number of things in this role (depending on the message load), including web services of various kinds, various IoT protocols, "raw" DDS, etc. Doing this in the general case is hard (see the eProsima Integration Service as one example) and the potential payoff of hand-crafted vs general-purpose translation depends on how much data you want to push around, how many datatypes, how frequently those datatypes change, etc.