It depends on the breed of rabbit, my regular bunnies could handle just about any thing,but my Angoras were very picky they needed to be 40-70 degrees below or beyond and we had sick and dying rabbits.When I moved from Washington to montana luckly it was spring, summer and they had time to adjust to the alttude and dry air here in Montana., from the moist air in Washington. They also had the fact they were only 6 months old.
Sorry to here about you losses, one yaer we had a run of very sick hampsters I think we had 7 die in a 6 month period. The kids were about 7years old I had more little graves in my garden I wasn't sure where to plant my carrots.