Hey Daniel,
I raise both species here in Southern-Middle-Tennessee. But, I do it in a 10-14 insulated bird house that I built. I've known a couple of folks who have smaller outdoor aviaries, but they seal them up and put in some kind of heating during the coldest of the winter months. I keep my bird house heated a little. usually the temp is between 48 and 53 degrees at night. I know from one commercial breeder that lovebirds are not going to do well in temps much lower than 50 degrees. I think cockatiels are a little hardier but I still wouldn't let try keeping them in temps lower than 45. Hopefully, you can find someone raising them in your area and see what they have done.
Good Luck!