It doesn't necessarily have to be a relative. Anyone who passed away who you cared about. If you haven't suffered that sort of loss consider yourself blessed!
My great grandmother, who I had never met but saw a picture of, used to come around me. If I was doing anything artistic as a child, I would see a very tall shadow of a woman come over me (she was 6ft tall) and smell the scent of roses.
Ancestors are still ancestors. Bloodline is very important. So it doesn't always matter if you knew them.
When you smell the roses, stay aware of any spiritual presences or other signs and cross reference it with family pictures, descriptions, etc of those who have died.
When a passed loved one is near me, I sometimes come across an old gift from them or photograph I had misplaced, or I'll find constant reminders that bring me back to old memories.
Those who have died that are closest to us remain the most illusive (most of the time). I have seen my husband's relatives but I never see mine.
We are not the only ones who feel sadness about death, those who pass away mourn losing their living loved ones just the same. So many times it is hard for them (emotionally) to make direct contact. Instead they give little signs that they're there, like the rose scent. Or they will show themselves to someone around you in hopes that they will tell you what they have seen.
My great grandmother was known for this (on many occasions). Here is just one. My grandmother told me that a few months after her mother died, a neighbor came to her and said "I saw your mother yesturday, I said hello but she didn't say anything back, is she alright?" Of course she was then informed of the death. It gave the family great peace of mind to know she was watching over them.