I added my parents (who have a single email account) as Granny and Grandad. When they logged in they then chose a name (my Dad Michael used his). We just got a notification saying that Michael loves a photo which freaked me out as I had shared it with Granny and Grandad - not Michael... so long story short I suggest you either add the identifiers we create in brackets every time a user notification is raised ie Michael (Granny and Grandad) loves this photo of <childname>, Or in the share screen when I login you show the name they created on inital login.