To me - all of them are natural, and mean the same thing. I think my preference would be 3,1,2. But - to avoid confusion, I suggest you are explicit about which winter! The Chinese winter or Australian winter?

"will" is used when you make a decision at the time of speaking. "Tom arrived home yesterday." - "Really? I'll go and visit him." "going to" is used if at the time of speaking you have already made the decision about what to do. "Tom arrived home yesterday." - "Yes, I know, I'm going to visit him tomorrow after work." "will be doing something" is used when you talk about a future activity which is going to take place at a certain time. "This time next week I will be swimming in the sea." Hope this helps.

The first sentence uses the future continuous tense and appears often in sentences with more than one clause: e.g. "When I next speak to you, I'll be lazing on the beach in Benidorm." You are telling the listener exactly what you will be doing - your activity - at a specific future time. The listener is more likely to imagine you on the beach (and feel jealous!).

We look forward to seeing you then :)

The third sentence is most commonly used =planning (80% surely) The second sentence is not as popular as (means you just want to go but have less plan) The first sentence is just used to emphasize that you are taking that action at definitely time (We'll be spending the winter in Australia so don't disturb us at that time)