To get the latest locations of your family members, just tap anywhere on the map (not on a family member)–the refresh and re-center buttons will appear on the lower right of the map. Just tap the refresh button to get the latest location data available for your family members.
The locations of other members of your family update as they move. If they're in a moving vehicle, you should see their locations update approximately every 5 minutes. If a family member has been in the same place for a while, the app may not update their location in order to save battery, but their location will update if they start moving.
There are several conditions that could cause a family member's location to stop updating. If their battery is low and their phone is in low power mode, the app will stop updating their location. If a family member turns their phone off, uninstalls the app, or disables location services, you may also stop seeing updates. The same holds true if they're in an area where their phone can't access the internet. Disabling wifi or push notifications may also adversely affect location performance.