I am having the same problem seeing dead relatives in my dream...I wanted to ask someone about this  and saw this thread and wanted to comment. I think our sub-concious mind is always alert and in some way communicating with them or they are trying to communicate with us. It may be just my imagination going too far. Dreams when I see them are always a troubled dream or too much confusion, so maybe associating some negative aspect in our life with the loss of our loved one triggers this sort of dreams...