The short answer
Measure usage by line, set sensible controls, and choose a plan based on the household's actual high-use habits.
Step by step
Review two or three billing cycles and identify each line's cellular and hotspot use.
Set device-level data warnings and carrier alerts below any high-speed threshold.
Move app updates, cloud backups, downloads, and high-resolution video to Wi-Fi where practical.
Use parental controls and app-specific cellular settings instead of imposing one vague rule on every line.
Recheck usage after a full cycle before paying for a larger plan.
Before you finish
Keep screenshots, receipts, chat transcripts, confirmation numbers, and the first bill after a change. Carrier terms and account eligibility can change, so verify the final price and conditions directly before submitting an order.