I am somewhat confused on a few things and also have a few questions.
What is the difference between necromancy-- talking with the dead-- and mediumship?
My family has long had a tradition, if it can be called that, of dropping by to check in on the family members wether they were dead or not. Grandma may come and play with the new great-grandbaby, even if Grandma passed 30 years before the child was born. It's "weird" tends to freak out the spouse and not talked about too much outside the family.
On the other side of my family, my beloved Granny passed over just over a year ago. I have spoked to her several times since. She let me know that she's ok. Said it wasn't what she expected, but that she was fine. It bothered me a little only because she's still in her house when I think she should have moved on by now. Can't tell Granny anything, even now. She'll do as she pleases.
When I was 18, I had an experience at her house that really got my attention. I was dead asleep when I woke up to Native American chanting coming from across the lake. There are no Indians there. From the next day onward, I felt the presence of an older Native American man standing behind me with his hands placed on my shoulders. I felt great comfort from him. Over the years, the feeling of his presence faded. I feel that this was probably my spirit guide. I hope to reconnect with him.
Any thoughts, opinions?

Mediumship is communication with the departed - dead in the physical body.  The spirit survives and it is spirit to spirit that communication takes place.

Necromancy may be a form of how this takes place.

We are often aware of our own loved ones, even if we do not open to mediumship and develop.  All life is progressive on earth and beyond, so it is important to encourage all spirit into the light.  Then communication can take place on a better level.  Our loved ones return in love and light.