Is it possible to have one server acting as secondary for two primaries on AG?
As I understand your question, the answer is Yes.  1 SQL instance can act as a secondary for multiple Availability Groups.  Listeners will point to the appropriate AG.  You may have some security concerns to address if the user base of the different AGs is a different set of users...make sure they can't access each other's databases in the case that they are read only, or acting as primary on the DR(Secondary) server.  Also, all instances will need to be a part of the same WSFC.