Normally speaking somebody is considered family if its to a maximum of the third degree so:

Parents, siblings, uncle/aunt, grandparents and niece/nephews.

Further down the line it is considered lineage Your lineage is your family "tree" and consist of all direct relatives in the male line (only siblings included, children of siblings arent the same branch but are of the same house)

so lets say, your greatgrandfather had 1 brother, this brother is considered of the same "branch" but all (grand)children of the brother are considered of the same family but not the same lineage. same things goes for the brother of your grandparents, its a uncle to your father and his son/daughter is a nephew/niece but the aren't youre nephew/niece.

For the female line (atleast in medieval Europe) only the parents/grandparents/siblings are considered direct relatives

Furthermore in some countries somebody is considered family if there is a bloodbond and they got the same surname.

From my understanding in CoE Family implies a direct family line, which is Husband, Wife and Children. A Cousin may be considered family but is not part of the direct line. So if family helps you return from the astral plane, don't count on your cousin or nephews to aid in this effort, it is only a direct line.

I'm new as well, and I didn't see a definitive answer in the Developer Journals. However, I think DJ5, DJ6, and "down the rabbit hole.." will give you some good information.

Personally, I think what has been said about lineage is correct, that skills/professions etc. will trickle down the line for all descendants of that family. But, I don't know to what extent that is changed by the ongoing actions of PCs and NPCs within the family.

That's assuming the game recognizes them as family forever, though. I'm pretty sure it's already been hinted at that contracts for kids will specify what family the child is a part of. But, since the child will use traits/attributes/appearance from both parents, I don't see why descendants of one family can't be vastly different in looks etc., several generations after.

Also, I mean no disrespect to Sullen, but I'm not sure one way or the other which family members do help you spirit walk. In the second paragraph of "spirit bonuses & talents" from DJ4, when they say "family" it sounds like the same "family" they use to include cousins when they talk about NTCs and heirs in "down the rabbit hole.."

DJ4 - "While it doesn't shorten the distance you have to travel to your body, having your family around you gives you a reason to live and strengthens your bond to the mortal world."

Down the hole - "It's important to note here, you don't have the capability to lock your siblings, nieces, nephews or cousins, but you can see their NPC codes. This prevents you from preventing NTCs from joining your family, but it does give you the ability to invite those people into your family who you want to be there."

Then again, those are ages apart form each other. So, what they consider to be "family" may have changed. Also, I'm probably missing something haha