Networking for Robotic System uses internal ethernet with no router typically, but can be connected to an external router I do not have access to

        <em>Note: I am a novice in networking. Also suggestions that do not require hardware redesign of the robot are preferential</em>

I am developing an open-source underwater robot (AUV), and my robot currently uses UDP to communicate data packets over internal ethernet wiring. There are 3 unmanaged network switches (embedded in the system), a SOC computer (Latte Panda Alpha, DJI Manifold 2, or raspberry pi 4) with 1 ethernet port and 1 wifi port, and multiple low level microcontrollers using a W5500 chip to communicate over ethernet in the robot. To avoid issues with the enterprise networking system at my university which requires each device get 24 hour approval to connect, I can bring the robot to my home internet. There, I can communicate between all modules, the SOC, and my personal computer using UDP. I have all devices on static IPs at the moment to minimize difficulty in connecting. I do have a few concerns for this setup when releasing the robot to the community. My preferred behavior of the system is this: When disconnected from an external router/internet, the robot communicates locally. When connected to an external router/internet (when the underwater robot is tethered), the devices continue to communicate to each other without interruption locally, and the SOC is connected to the router/internet. I would also like to be able to connect the SOC to WIFI to SSH into the device when the robot is on shore, and keep the internal devices communicating locally. I am concerned about an external router not accepting the static IPs, or possibly changing them, and the robot losing local communication. I am also worried that an external router will block the UDP packets. I can add some router software to the SOC, or change from UDP to a different communication protocol, or something else, but I am not well versed in the actual networking to know the best configuration for such a system. I also cannot add a full commercial router into the system as it will not fit. In short:

1. Can i communicate among all devices locally onboard without a router? (if no, i can add router software to the SOC).
2. If I connect a router (that I have no access to), how do i keep local communication functioning?
3. If i wish the SOC to have internet over Wi-Fi, and communicate locally using ethernet, is that possible?

Any help/suggestions would be greatly appreciated!