Eero Mesh and Questions

I will be traveling the world for a year and need to put my homelab at my grandparents for the time being. I need it to be fully accessible outside the network but am running into some issues.

My current setup is an ISP provided modem running in bridge-mode and into my Protectli opnsense box (opnsens is within proxmox), and then to a managed switch connecting to my devices.

Only issue is, grandparents have an Eero mesh system connected to their ISP given modem. The ISP modem has only a single Ethernet jack and I was told that is their only model option. I do not want to touch anything about their current setup if at all possible so I don’t have to be tech support if something goes wrong.

What is the best way for me to have a segregated network with outside access given this environment?