Yeah it's cold but with a sweater you can totally take them outside. I would definitely try that. If your eventual goal is to get them to go outside I wouldn't let them go in the house any more. That will be a hard habit to break later. Mine go outside - heck they even went outside when we visited my brother in Wisconsin last Feb. with 3 feet of snow. Really, it's OK. I don't even put a coat on Loki now that he is so efficient (in and out in 30 seconds, he's a professional pee-er
) Sam needs a sweater or something (she's a skinny butt with no body fat!) and she will stay out there until she starts to shiver (by choice, she likes to sniff stuff) but she warms right up when she comes in. I'd say if they can warm up in a minute or so after coming in then it's probably fine to send them out there. Good luck!