I wouldn't be comfy at all using DE in the house for a couple of reasons. Full protective gear is recommended even when using it outside, no less exposure inside where the particles can be airborn and inhaled or other. There's really no way to get rid of fleas short of treating the animals, covering dishes & food stuffs, and setting off bombs at the recommended times and washing everything.
I feel for you...I had a newborn (human) baby when my young son, bless his heart, brought home (unknown to me at that moment) an abandoned flea infested kitten for me to save and brought it inside for only a few minutes before I was even aware and then moved the kitten outside and made a vet appt for him...well, within several days we were infested, with an ill newborn baby an mom in the house. What a total nightmare the next couple of weeks were.
There's really no "natural" way to rid a house or animals of fleas. Hoping you're able to find a solution that works out for you.