First: you can subscribe to n simultaneous streams/downloads. Ours is 2, and sometimes the kids complain, and end up sorting it out somehow.*
Second: if you have a kid at college, they "live at home" for various other mechanisms (count as a dependent for taxation; qualify for parents' health insurance, can vote in their home district regardless of where they live; can be part of a family phone plan, family apple plan, etc etc...)
* And third: they don't seem to argue about netflix much any more; I think if I dropped the sub to a single session everybody would still be fine. Netflix seems to have an increasing density of junk content, losing its distinguished position.