OMG 19 degrees inside the house?! Brrrr! I didn't think you were talking about temps below freezing *inside*!
I think they'd be ok - maybe not comfortable, but ok - as long as they had somewhere to snuggle up to conserve body heat. And I would definitely leave tons of food out. The stray that I feed, who has a nice house, with a heated pad and bed inside it, eats much more in the winter - he probably gains nearly 2 lbs. In the warmer months, he slinks through the slats in the railing to get on the deck, but in the winter, he has to jump on top of the railing and then back down because he doesn't fit. LOL.