Can you tell me a bit more about it. Please. Its no harm, I'd just like to know why it visits them.

Perhaps it is someone who has a message for your family from the realm beyond? Just guessing here...

Are there any occurrences that have been significant in your family that might have precipitated the appearance of the entity?

Do they know who it is, or is it a stranger ?

You imply that each time your family member has been alone when they've seen this spirit person, is it possible that they could reinact the situation when the spirit was seen ,but be together, although it never seems to happen this way, but it's worth a shot.

If they were together maybe they could speak to the spirit and ask if they could help them.

Could it be a family member that is just watching over you ?