Guest Network

I just moved to the middle of nowhere and Ziply DSL is the only basic internet option that is more reliable that Hughes Net Satellite and cheaper than Starlinik... I'm using their router and their extender. We have someone that lives on the same property as us wanting to use it as well. I don't have a problem doing so as long as it isn't slowing down when I'm trying to do things. However I don't see any router admin password in my account info, any sort of guest network options or way to control who's connected? Is there something I'm missing or is this not possible?? How can I allow them access to wifi for their phone use without being able to cut them off if a time comes that they're slowing down my connection too much?