Dogs mourn the loss of another dog too. I remember my first 2 huskies Dakota and Simba. When Dakota passed, Simba used to have a seizure on the day of Dakotas death for the next 2 years. The doctor even didn't seem surprised by it. He had one exactly at a month, then every year. Never had a seizure other than then. Vet said they know...they stress.
With my youngest off to Japan my big concern was the dogs stressing out. He was around the house with them ALL the time. We've been trying not to seem stressed just so they wouldn't pick up on it.