My grandmother is hearing the voice of her late husband calling her at night. She isn't sleeping. Is this common?

Your grandmother may have a very good memory about things that happened long ago, but that doesn't mean she can make new memories now. As for her sleep, likely she is sleeping more than she realizes. Perhaps, she sleeps quite a bit in the afternoon, or the following morning.
I don't want to be alarming, but she is 93 years old. She's lived a long life. It's not beyond some understanding (in my experience with end-of-life situations) that she feels her husband "calling her." She may be preparing herself to leave this body behind.
However, I do think the rest of the family should be told the story because people do sometimes decide on some level that they've had enough, so to speak, and then their family finds that they "suddenly" died. Many long-term elderly couples die within days or weeks of their spouse. Their reason for living is gone.
It's possible that your grandmother will continue to live for some time. If she's not physical or mental pain, that's good. But do prepare yourself and your family for the possibility that her life will soon be over.

Take care of yourself. You sound like a wonderful grandson.
Carol

How is her hearing? I get minor "auditory hallucinations" sometimes - thinking the phone is ringing, etc. When your ears don't work quite right, sometimes the brain tries to fill in the blanks.

Get her to the doctor to rule out a UTI, which can cause hallucinations, or any other acute illness. Have the doctor review her medication for anything that might be causing this.

To help with her emotional distress, ask her if she would like to write a letter to her husband, to let him know what has happened to her, and how much she misses him. Of course she can't send it, but she might enjoy communicating with him.

my mom is 83,she has dementia.She says she is not sleeping,but she sleeps.I think they forget they slept..