Airlines routinely select their wines and foods to account for taste differences during flight, nothing that they taste typically less sweet in the air, although this is more to do with the in-flight conditions - pressurized climate, dry air dehydrating passengers, harsh light, engine noise etc, all go to affect the perceived taste of the wine and food.
In your case, going from 300 to 3000 feet in itself doesn't make any significant difference to the beer itself, but you may perceive it differently, especially if you're not used to being at that altitude.
It could be in part that you were just being more critical since you were tasting in front of family/friends. Taste can very from day to day according to many factors such as how you're feeling, your state of health and what you've previously eaten and drank that day.
But having said that, your perception that the beer was sweeter ties in with practices for high altitude cooking (3000ft and over.)
Sugar adjustments: Although I really don't understand why, I do know
that I often have to reduce sugar in some recipes. For high altitude
cooking, this guideline really does work to make cakes and cookies
taste better: for every cup of sugar you'd normally use, reduce that
by 1 tablespoon at around 3,000 feet to as much as 3 tablespoons less
at even higher altitudes. It does make a difference in the taste of
your final product!
So you may have to start making the beers a little more fermentable to reduce the overall sweetness if you're planning on drinking them over at your parent's place, or have them come to you instead and see if the beer is the more in line with how you expect it to taste.