The story of Airavan and Mahiravan abducting Rama and Lakshmana is found in Ananda Ramayana. They are two different persons.
I have written answer to Who were Ahiravan and Mahiravan? .
The source of legend of Airavan and Mahiravan is Ananda Ramayana. It is part of story of Rama which is spread in vast expanse (Charitam Raghunatasya Shatakoti Pravistaram). According to that text, both the Rakshasas were slain by Lord Rama.
Hanuman devised a plan to remove the immortality of Ahiravan and Mahiravan by destroying the honey bees which were providing nectar to Airavan and Mahiravan's blood. I explained that story in detail in my other answer.
tato nihatya tau daityau punarbāṇai raghūdvaḥ।
amiṣicya tayo ḥ sthāne rājye taṃ makaradhvajam ।।
Rama killed those two daityas using arrows and consecrated Makaradhvaja as ruler. (Verse 122, Sarga 11, Sara Kanda)
Answer is based on Hindi translation of Ananda Ramayana by Ramtej Pandey.