Your question is Account Sharing Detection. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
How would you figure out if two households are sharing an account?
Explain how you would distinguish legitimate travel, second-home usage, and device changes from likely sharing. Treat this as a practical analytics exercise: define the metric, identify the data needed, describe the analysis, and explain how you would validate the signal without penalizing legitimate members.
Assume access to account, profile, streaming-session, device, location, playback, and customer-support data.