- How hard is it to follow the trail in the dark? (We will be hiking in the dark for 4 hours from 2am to 6am until sunrise) A bright flashlight should be sufficient?
There is a risk of losing a trail. I lost the trail the first time I was there in early May
You need to have either a map and a compass and a good understanding of the logic of this trail or a GPS with a preloaded trail map
- Do we need snow axe? (I have never used one before. I am not sure if we need this due to the low level of snowfall this year, and we are going in late May which is almost summer time.)
You do not need an ice axe in case you never used it. You can hurt yourself.
- What is the chance that we will get high altitude sickness? Is there any medicine we should bring? (Both my friend and I hiked Half Dome before and didn't get sick. But again Half Dome is only 9000 feet, while Mount Whitney is 14000 feet.)
Nobody knows in advance.
How many days do you plan for you acclimatization?
What is the difficulty hiking Mount Whitney, comparing to Half Dome? (From what I heard: Half Dome is 17 miles / 10 hours with some climbing on steel cables at the end, while Mount Whitney is 22 miles / 15 hours class 1 no climbing... Does this sound about right?)
What was your Half Dome time?
For me Half Dome hike (with cables down) was easy. However twice I turned back from the Whitney Crest.

We are planning on bringing 2-way radios so that we can talk to each other in case we get separated (though we try to stick together the whole time). Is that a good idea, or is there any other suggestion?
I am not sure whether FRS/GMRS radios would work over the crest.
Bring them (they do not weight a lot) but do not trust your life to them.
A better suggestion is to hike together as a group (in case you have similar endurance).