I have them in our lounge with a heater in the room, set to turn on early in the morning to take the chill out of the air. Our temperatures are so very cold at the moment with snow in southern parts of the country. We live in the far north of New Zealand where there is no snow, however our morning temperatures are coming in at a very cold 6 degrees Celcius (42.8 Fahrenheit) in the morning.
Just look at big caterpillar in the picture above. At one stage I wondered if it would even survive, because it was quite sluggish when I found it on a swan plant outside in the cold, several weeks ago. Now it's growth unlimited as it steams towards being large enough to form its chrysalis quite soon.
........and, the other two caterpillars are doing just as well.
Small caterpillar is rapidly heading towards being a large caterpillar. Tiny caterpillar is now medium in size. I place their plant in the sun coming through the window, during the day, and the heater warms them the rest of the time.