FINCHforum

I am not sure which of your finches would be hardiest other than the zebra's because I have never owned most of those species.
As far as getting sick more often you may have to treat with a preventative more often I don't know. You do need to take into consideration other predators. I know some places that have to have the flight/aviary off the ground and use 1/4" galvanized wire because some snakes can get through anything larger than that. In other places you need to place wire 2 feet or so underground to prevent predators digging into the flight/aviary.
IMO it is probably best moving them in the warmer months so they can slowly acclimatize to the colder weather.
In summer months you need a shaded area for the finches to get out of the sun if they get too warm.
In winter I have heard of people having a closed off building attached to the flight for the finches to stay in with a heater and I have also heard of people wrapping the flights in a type of plastic insulation and using a heater inside if needed.
Lastly again this is just my opinion but it is probably better to wait till the babies are older? Because their immune systems are so under-developed?
Thats all just my opinion. I have no experience with keeping birds outside as it is way to cold where I live. Everything I have said has been from talking to other people that have done this.

This is not the time to introduce bird to the outdoors, espicially young. Our weather is to cold at night and the temps are over the place during our winters here. I am about 30 minutes north of you. Introducing birds to outside should be done in the mid Spring. I advise not put young bird, any birds that are use to indirect temps outside at this time.