Are all of these possibly Hoyas? I'm just guessing here.
My suggestion would be to check with you Vet? And online you could check the ASPCA...
http://www.aspca.org/pet-care/...
Hope this helps. And
to ATP
And I found this also...
http://www.babycenter.com/404_...
I could be wrong, but no, I don't believe Hoyas are toxic.