A true multi-user “family account” with shared editing is uncommon. On many photo services, one user generally cannot edit another user’s albums.

Based on the suggestions here, the practical options are:

• Use one shared account and give family members the same login if you specifically need everyone to edit the same albums.
• Use Google’s sharing features (such as a family-only circle/group) if you want private sharing and good compatibility with Picasa/Google tools, though that may be more about sharing than co-editing the same albums.
• Use Dropbox if collaboration matters most: its gallery features are basic, but shared folders/albums are easy for multiple people to contribute to.

So if your priority is collaborative contribution, Dropbox is a simple fit. If your priority is staying close to Picasa/Google, Google sharing features are the most natural place to start. If you need full mutual album editing on one service, a single shared login may be the only straightforward option.