Can my family see my photos if I sign up for family sharing

Actually a Shared Family photo album is a feature of Family Sharing. Photos need to be actually shared through that album to be visible to other members of the family group however.

So unless you actually share you photos, they cannot be seen by anybody else.

Set up Family Sharing - Apple Support

Is that still the case when you are sharing iCloud storage?

No, that is not a feature of family sharing. But, if you want to share pictures with your family, you can do so with a shared iCloud Album. You can learn how to create one here.

Yes. You are only sharing the storage for them, not the photo libraries themselves.

Other people in the group cannot access iCloud Photo Libraries from other members in the family group.

If you don't have iCloud Photo Library turned then, then your photos are not even on iCloud.