You can share a calendar with someone else. If you go to the settings page (on the Google calendar site, not on your phone), in the row for your calendar you should see a link to "share this calendar". Plug in the sharee's gmail address and choose the level of access you want to give them, and then they can see your calendar in theirs (it may actually send them an email verification link first, I don't remember); they can assign it a different color or whatever, and turn it on and off as they wish (just like everyone can with their own calendar or the extras that Google provides).
I did this a couple of times: I created a separate gmail account for my softball team and shared it with everyone on the team, giving my own gmail address full control over it so I could change it from my own gmail login. I also am an assistant high school debate coach so I created a subcalendar under my gmail account and shared it (read-only) to my girlfriend so she isn't constantly asking me "do you have debate stuff this weekend?".
After setting up the sharing stuff it will take a little while to percolate over to your phone(s); you might be able to force a Google account refresh to speed up the process. Since every calendar app/widget seems to be different, I don't know what to tell you specifically, but you're looking for a "calendars" menu item or screen. You should always be able to see your own calendar as an option to view and/or sync, and once the share settings have been refreshed you should be able to see the other shared calendars.