Important note:

This process will only work if you specifically haven iCloud Mail account (ending in @iCloud.com). If you are using the Apple Mail app on your computer of phone for your email, you'll need set up forwarding directly with your email provider (example: Gmail)

Step #1:

You'll need to go to icloud.com/mail and log into your account.

Step #2:

Tap on the little gear sprocket and then navigate to "settings".

Step #3:

Navigate to "forwarding". You'll want to tick the box and enter you family email address (as seen below).

You'll just need to tap the little "x" when done.