I'm a father of two (soon three) and I love Opeth. Been listening to them since they released Orchid. My wife and kids also love Opeth, growls and all. All four of us actually went to see Opeth live a few years ago.
So, yes: There are parents that love Opeth. Even the growls. And yes, there are female Opeth fans.
I started listening to death metal almost 20 years ago, so the growls in Opeth were nothing new to me. And I don't think I'll ever grow tired of that kind of music.