I am so sorry! I love those two boys and hate to think of them having a hard time

I am sure the feathers will regrow and Beaks will be back to his majestic self.
I know very little of your birds' "logistic" situation, but is there any chance of you being able to take them with you at your moms' when you know that dad will be away for a while? They could stay in a smaller cage, the large carrier type, and you'd be able to keep an eye on them for those few days.
If this is not an option:
When I moved the birds lately they had a couple of frights due to the new environment, new shadows, noises etc, so I introduced a 3watts light (equivalent to 25watts of the old type), very feeble but stronger than the small night light they usually have on at night.
It made a lot of difference! And these 3 or 4 watts are very inexpensive because not many people need them in their houses (they are really weak)