What is the meaning of Brahmarakshasa and how is it different from Narasura, Rakshasa, Asura etc?
Is Ravana a Brahmarakshasa?
A partial answer.
When does one become a BrahmarAkshasa?
Samyogam patitaira gatvA parasya eva cha yoshitam |
Apahritya cha viprasvam bhavati brahmarAkshasah ||
Manu Smriti 12.60. He who has associated with outcasts, he who has approached the wives of other men, and he who has stolen the property of a Brahmana become Brahmarakshasas.
So, this is talking about afterlife.
Brahm Rakshas is actually the spirit of a Brahmin , a dead scholar of high birth, who has done evil things in his life or has misused his knowledge, who has to suffer as a Brahm Rakshas after his or her death. The earth- bound duties of such a scholar would be to disperse or impart knowledge to good students. If he did not do so, he would turn into a Brahma Rakshas after death which is a very fierce demonic spirit. The word Brahm means Brahmin and Rakshas , a demon. As per ancient Hindu texts they are powerful demon spirit , who have lot of powers and only few in this world can fight and over-come them or give them salvation from this form of life. It would still retain its high level of learning. But it would eat human beings. They have the knowledge of their past lives and vedas and puranas . In other words, they have qualities of both Brahmin and Rakshas
your another question about ravana ravana was a rakshasa .rakshasas were born to a great sage, Vishrava (or Vesamuni) and his wife, the daitya princess Kaikesi so all children birn to kaikasi were rakshasas and Ilavida the another wife of sage vishwara was kubera.