I would say neither PPPoE nor Hotspot. I work for an ISP that uses PPPoE to service customers, and it works great for us. For you I think it is completely the wrong option. PPPoE setups usually assume that the end customer has a router of their own. Smartphones do not usually even have PPPoE stacks in them, so the only way your tenants would be able to get their smartphones to connect would be if the tenant plugged in their laptop, connected it to your PPPoE, and shared the Internet from their laptop to their phones (creating their own access point essentially). This is too complicated. With a fixed number of customers, hotspot is also unnecessary.
Just create four different VLANs and four different SSIDs and use RADIUS authentication for wireless. If you only have four apartments, then you have a fixed number of SSIDs/VLANs to configure. It is not difficult. PPPoE would make sense perhaps if you had hundreds of apartments, but for four it is complete overkill.