I believe so. When my male Dalmation died, my female mourned for weeks. She wasn't herself, she howled every night, didn't eat as well...most people will readily say that this is simply due to the change from pack-environment to sole dog, but with the other dogs we had before she died she never was as close to them as she was to Rosco. When my cat died a few months ago, Mudflap and Nick looked for him for weeks. They both still look around in his normal napping places every now and then.
When I'm gone for lengths of time, my dogs look for me, and when I get home they are overjoyed to see me. I think they do get attached to each other and to their human companions, and they miss them when they are away, or when they die.
Of course they have.
They can be scared, really scared, they show when they are happy, when they just want to be silly, excited when they see we are going somewhere, etc.
Like when Pami is sad, she hides under my bed (Like when I'm going to school).
I allways say that they are almost humans, except for talking. If they had the ability to talk, they would be completely humans.
I've had two dogs go through terrible grieving after losing another of our dogs. It was made more obvious when we got our last foster just after our 9 yo Golden passed. Our girl perked up and enjoyed being out and playing where she just slept by my chair the previous weeks. She was actually careful and encouraging when the foster was very fearful.
We have an 11 mo puppy now and when I crate puppy with a kong for an hour or so she transforms into a dog on vacation. Happy and displaying behaviors that I didn't realize she was not doing because she does love the puppy. She'll try to get me to play more and just daydream on the deck when she knows puppy isn't stalking her tail.