While product recommendations are generally off-topic here, there are a couple types of solutions that you can use. Some are more practical than others for home use.
- Dedicate one computer to run software that tracks data usage across your local network. One fantastic solution for this is NetLimiter Monitor. It can track just on local client, or traffic within your local network. Paessler also makes freeware that can do similar tasks.
A similar question was asked here, credit for this part of my answer goes to Molly7244
- Routers typically have a built-in traffic monitoring log. While this typically isn't very comprehensive, you can find routers that have more robust traffic monitoring tools built-in.
Most hardware solutions will be geared towards corporate networks, and most of the time will simply be overkill in terms of features and way overpriced for a home application.
Some hardware firewalls have built-in bandwidth monitoring. I have friends in IT who have recommended Fortinet appliances for QoS and bandwidth management.