1) Why Hazrat Abdullah Ibn Jafar was not present in Karbala?
2) Why Hazrat Mohammad e Hanafiya was not present in Karbala?
(I have heard that he was ill but Hazrat Saeed and Muslim ibn Awsaja were also old and they don’t have strength but still they were present in Karbala)
3) Why Abdullah Ibn Abbas was not present In Karbala?

Difficult to search reasons for the historical events.
What we understand from some of the narrations are as follows

1. Yes they were ill.
2. They had responsibilities from Imam to stay in Madina and Mecca to control the situations and inform Imam accordingly. This has been mention for both Mohammed Hanafiya and Ibne Abbas. And for Abdullah the first reason is known.

Allah is all knowing