The short answer
Compare the host network, each line's data needs, family pricing, hotspot rules, and support before choosing a lower-cost carrier.
Step by step
Map each family member's real monthly data and hotspot use from the last two or three bills.
Identify which major network performs best at home, work, school, and regular travel destinations.
Compare the total multi-line checkout price, including prepayment, taxes, activation, and any introductory pricing.
Check priority-data, hotspot, video, international, smartwatch, parental-control, and device-financing terms.
Test one line first when possible, then transfer remaining numbers only after calls, texts, data, and voicemail work reliably.
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.