hey MQ-S
i can't speak to this from a spouse perspective, but i can from a son's. my dad was diagnosed with terminal cancer in january 2017. he passed away in september of 2017.
there was the initial 'shock' of "oh man... my dad is going to die" which was tough (even though i know, life is finite, but just that we knew it would happen sooner than later).
i then made the choice that i was going to do everything within my power to support my dad and mom thru that time. it was tough, there were lots of tears, but those last 8 months with my dad were awesome and he knew with out a shadow of a doubt how much he meant to me.
i think that is the advise i'd recommend to you as a friend, support them however you can thru this tough time... but don't stop after the one spouse has passed away. the surviving spouse will be emotionally drained - do what you can to help them. one thing we have done since my dad died is have my mom over for dinner 3 nights/week. she loves it, our kids love seeing grandma and it's a few meals per week that my mom doesn't have to eat alone. these aren't crazy huge dinners (well... some are... but lots are just 'another portion' added to whatever we are having for dinner that night) and it's not like it's a huge visit - my mom will show up around 4:30, dinner at 5 and she's usually headed home by 7.
your situation is of course different, but just 'being there' for your friends and addressing specific needs would be huge.
another huge thing is the attitude of the couple - both the spouse who is sick and the one who isn't. my folks chose to make the best out of a crappy situation and thoroughly enjoyed what time they had left together - and i know that helped a lot.
don't be afraid to come here and ask questions - i had never been thru losing someone close to me so i asked for advise:
https://forum.calgarypuck.com/showthread.php?t=159736
this community was awesome with ideas and support
also - if you have any specifics you'd like to ask, feel free to pm me