Everyone on the dead is eligible for the AP perk for themselves and everyone else living at their address (up to 8), even if the people on the deed live at different addresses. However, it has to be a direct purchase, and someone at each address has to be on the deed to be eligible.
When we purchased our second direct
DVC contract, which was at BLT, we had myself, my wife, and both of our children listed on the deed as co owners. (they were both over 18 at that time). When we made that BLT purchase, we also paid to rewrite and have our two children added to the deed on our first direct contract, which was at BWV, that we had purchased when they were under 18.
Now both of our children, as well as my wife and I are all eligible for all "perks" of being direct owners, (since we are all members) despite the fact we live at different addresses. Those perks include all of us being able to purchase AP's at the DVC rate for ourselves and everyone else living at our addresses.
Not sure about the limit of 8.
Whether it per address, or per membership? (however, based on what Sandisw said above it appears to be per address (household)
For example, not sure if our daughter (who is a member), her husband and potentially their 3 children who all live at the same address, could purchase 5 AP's, and our son (who is a member), his wife and potentially their 3 children who all lived at a different address could also purchase 5 AP's, and my wife and I could also purchase 2 AP's, for a total of 12 for the membership, but not more than 8 for each address.
Not an issue currently, since we have only 2 grandchildren, so there are only 8 of us in total.
Hope that helps
ETA: see
@Sandisw post below, where she verified it is 8 per address.
Also, FYI: my wife, myself, and both of our children each have our own "blue cards"