How to Gather Information on a Mac Adress Without Being in the Same Wireless Network

Hi.

I know how to put my wifi interface into monitor mode and how to use airodump-ng to gather information on the mac adresses that access an AP. But the mac adresses are not realy expressive. Even if I know that an iPhone and a PC are connected to the AP, I would still not know which of the MAC adresses is assossiated with the devices. HELP! Thanks in advance