Interceding to convince the killed person's family to pardon the killer
There is no blame on doing so In sha’a-Allah (if Allah wills). This is because
pardoning the killer instead of demanding Qisas by those who seek revenge is a desirable practice in Shari`ah (Islamic law). Allah (Exalted be He) says in the Ayah (Qur'anic verse) revealed on Qisas: (Part No. 21; Page No. 212)
But if anyone remits the retaliation by way of charity, it shall be for him an expiation.
(may Allah be merciful to them) related on the authority of
Anas (may Allah be pleased with him) that he said:
"The Messenger of Allah (peace be upon him) did not judge in any dispute that involved Qisas but he commanded pardoning (the killer)."
It is worth mentioning that there is no Nas (Islamic text from the Qur’an or the Sunnah) that prohibits Muslims to intercede in Qisas. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.