Although I haven't lived at home (near my parents and DB) for many years, my DCs and DH and I visit often and we are all very close.
Their dear old girl is now 15.5 
and her back legs have just failed for the second time. She's had a stroke before but after relentless love, affection and exercise my DB helped her regain the use of her back legs at that time. Now, she's very old, has cataracts so can't see very well, she's quite deaf and generally a very tired old lady. They're heartbroken as they fairly certain that when they see the vet on Tuesday he's going to tell them that it's time.
I'm not currently a dog owner but I ache to see the depth of their grief, this was pretty much my DB's child and my parents were devoted to her also. I never really lived at home while they had her but she's a lovely dog and we're all going to really miss her. 
I just don't know what to say or do. They're devastated.