Hello,
Sorry for this invasion into your family. Glad you found this forum.
From this PALS perspective -
DO acknowledge the ALS (but he's still the guy you knew before diagnoses)
DO listen but resist the urge to try to fix him or citing off the wall "cures"
DO support them with actions- not just words
DO be yourself - love him as you do your daughter
Don't just ask, what can we do? That is too broad a question to pose when people are in crisis- might be better to say "we were thinking of doing such and such- on this or that a day- would that be helpful to you both?" Concrete things- cleaning, meals, babysitting,
vacation getaway gifts, financial assistance etc. will be well received and remembered.
BE an ear. Have a big open heart and, if you can, wear it on your sleeve. It's OK to cry with them and even better still (in my world), to pray for them and with them.
It's not easy for families- it's indeed catastrophic- but ALS is not without its silver linings. There are many. Hopefully, you will discover some of your own, as my family has done.
I wish you the best.