Full disclosure: I work at Google (not on the Photos product though). All opinions expressed are purely mine, and not of my employer.
Api,services are being shut down and this time people don't even have 2 months to move. Picassa and Google Photos are 2 different products, if people stuck with Picassa there must have been a reason.
Without grahamburger's hack of creating an independent, shared account (which I wonder whether is strictly allowed by account usage terms), how can a family share all of their photos? I'm not talking about sharing an album. My wife and I would like all photos taken from either of our phones be automatically uploaded and shared between us. We've not found a way to do that using Google Photos without making everything public, which is unacceptable.