Photo-sharing feature of the iCloud is very confusing but you can always find some steps in order to know the things. Here are some steps that will help you to share photos to iCloud using photo-sharing feature.
Select the photos that you wish to share using the iCloud in the first step.
Once you are done and selected the photos, now, click over the share button.
Now choose photos from iCloud photo library and select the family album.
When you are done with the steps and the images will then sync over the family member’s device.