NB: This isn't a question about degrees of bloodlines (as signified by the "m" word).
The Grangers produced 1 child with magic ability, are they a wizard family? The Evans' produced 1 child with and 1 without magic ability, are they a wizard family? (I believe both of these sets of parents have no magic ability, I can't find anything to the contrary.) Lily & James Potter produced 1 child with magic ability, and had magic themselves. Were James Potter's parents magic users?
Is it definitely stated that a wizard family must have 2 magic parents?