We've told my father and he wasn't at all shocked about it. Well, quietly positive would probably be the best description.
He said that it was our life and we could choose our own relationships like we wanted.
He has yet to actually meet BlackUnicorn and VanillaIce but I don't really have any fears about it and I'm sure they'll get along just fine.
My sister was a little more skeptical about the situation but was willing to wait and see how it works out.
We haven't yet directly told Windflower's parents but her mother kinda knows we're poly as she noticed we belong to a polyamory group in Facebook. Windflower said she'll break the news eventually but for now she still wants to keep it her own sweet little secret