I agree with this, the only thing is that I've experienced assisting with all this goo and on one of the eggs I tried to take it out and assist so much that the goo dried up and stuck to his wing and head. He didn't die but it made things so complicated trying to wash off the goo, and he had wry...
Ah, I'm sorry. It is still possible that it could be twins. Either way don't lose hope! He's better off breathing outside the air cell than drowning in the egg.
I've only incubated goose eggs once so I'm not entirely sure how the air cells should look at a given time. In what way(s) were things not going right?
If he is near drowning because the humidity is so thick you could very slowly start to lower the humidity, maybe by 5%. Although 60-70% humidity is around the range it should be at in lockdown. Do you have a separate hygrometer you could put in to double check the humidity? Just don't make any...