How to Share a Family Calendar on the iPhone with iOS 8
As part of iOS 8, Apple added a Family Sharing feature that lets you share a calendar with up to six family members. This family calendar shows up in the Calendar app of each participating member of your clan.
The requirements: One adult in the household (a.k.a. the family organizer) invites everyone else to partake. Everyone must be signed into the same iCloud account. Family Sharing works with iOS 8 devices, Mac OS X 10.10, Find My Friends 3.0, Find My iPhone 3.1, and iCloud for Windows 4.0.
Because Family Sharing is designed to be used by only a single-family unit, you can be part of only one family group at a time, and you can switch to another family group only two times a year.
Each participating family member can add or modify events in the family calendar and receive notifications, alerts, and location-based reminders.
Family Sharing extends well beyond the calendar too. Family members can share photos, music, books, apps, their respective locations, and even the location of their iPhones (and other devices). Through the Parental Controls feature, the family organizer can limit the content that minors can access.
To get started, tap Settings→iCloud→Set Up Family Sharing. The family organizer enters his or her iTunes credentials (and payment method), and send emails to invite family member, who will be invited to participate.