Sorry to hear the reaction did not go well. Hopefully they will get used to the idea with time.
What amazes me is that you told them before actually having a second partner. My hat off to you for the guts you've got. I never actually told anyone in my family a thing about poly...I figured it was too complicated for them. When I had two ongoing partners, they of course eventually found out but I kinda just framed it in a different way of "yes I'm seeing them both" and left it at that to keep it simple.
Other than a gay uncle I got, I don't think I could ever talk about the p-word to any family. But kudos to you for going there!