Once your flight is cancelled, you may be immediately rebooked on an alternate flight (with United, I’d say that’s actually likely). So it’s important that all members of your party are linked together so you all get rebooked to the same flights. If you didn’t buy your tickets all together in one transaction, I’d call the airline now and have them link them.
Also, put the United app on your phone, logged into to your account with notifications on. That’s often the first way I find out about cancellations.
You want to be ready to make decisions and changes asap after you find out it’s cancelled. Be familiar with the United schedule, or just print it out ahead of time to refer to if you need it. That way you can know right away if what they rebooked for you to is acceptable. If it’s not, act quickly, get on the phone to United, go to manage your reservation online, get on a chat with United, or if you are at the airport, get in line at a ticket counter or gate agent. Your goal is to rebook on better flights as fast as possible. You are competing with all the other displaced passengers, so acting quickly can be really helpful.
Here’s a webpage with some useful info from United about changed flights
https://www.united.com/ual/en/us/fly/help/faq/schedule-changes.html
and here’s a page with some contact info including how to start a chat, which can sometimes be the fastest
https://www.united.com/ual/en/us/fly/customer-support.html
Hopefully, you don’t need any of that info and you’ll have an uneventful flight.