You shouldn't need any agents aside from the initial deployment of defender for server:
"When you enable Defender Cloud Security Posture Management (CSPM) or Defender for Servers P2, agentless scanning is enabled on by default."
As for the 3 agents you mentioned:
#1 is old, #2 (AMA) is new, and #3 is the Defender for Server agent.
At least that's my understanding.