WOW
that is scary. I've only ever seen one fox in my neighborhood and it wasn't anywhere near my house luckily. my yard isn't fenced in and i let morgan out without a leash while i stand in the door way watching. before i let her out i do a scan of the yard for animals but you can never be sure something isn't out there lurking and hiding.
I'm so glad you were able to get both babies back in the house with no harm from the fox. i dont' think he was rabid because he was actually stalking her instead of straight up attacking the dogs and/or you. Regardless its still really scary because they are so much bigger then our dogs and they can carry diseases. I think mange is also effecting many foxes.
You did a great job! a very scary situation but your protective instincts kicked in and you got those babies out of there.