How can I hide photos from family sharing

If you're truly using Family Sharing, where you all have separate iCloud IDs and one (presumably yours) is the "Organizer", then the only photos that others will see are those that you specifically share with them. Enabling Family Sharing turns on a "Family" photo stream that you can each contribute to, so you'd have to specifically add something to that folder for others to see it. (The only other way is to create a Shared Photo Stream, which is essentially like the Family one except with a Shared Photo Stream you can add people outside your Family circle.)

So to answer your question, if you don't want others in your Family circle to see a photo, don't add it to the Family photo stream. Family Sharing does not mean that the family will see automatically what is in your Camera Roll, Activity, or My Photo Stream.

Now, if you're sharing an iCloud ID (which is not what Family Sharing is) then all bets are off, they can see whatever you see (aside from Camera Roll photos you may have removed from your Photo Stream).

Finally, there is a new "hide" feature in iOS 8 ... just tap and hold a picture to bring up that option. But that only hides the photo in "Moments, Collections, Years" timeline, but not from your Camera Roll or any Photo Stream.