Viola and violin are close enough instruments that they can be considered the same for most discussions -- so technically, the "violin-family" tag is more accurate than the "violin" tag, but I think the former is inevitably going to fall out of use simply because it's an unwieldy term.
Case in point, there are currently 6 questions tagged "violin" and 4 tagged "violin-family".
There's also no "viola" tag (I tried to start one earlier but I didn't have enough points), and that's likely to become neglected.
What should we do?
Edit: I forgot to mention, the reason I bring up viola is because most questions regarding viola can be answered by violinists, but a lot of violinists likely won't see questions tagged "viola". In that sense, a more general term like "violin-family" could be better.