Sadiq Ahmed and Abid Hussain were being questioned in connection with the HuJI e-mail, they said.
The two are close relatives of surrendered militants Irshad Ahmed and Farooq Ahmed who have also been detained, the police said.
As many as 11 people have been detained so far in the e-mail case, they said adding over 50 people, mostly students, have been questioned so far.
Hours after the blast outside the Delhi High Court on Wednesday last, an e-mail was allegedly sent by Pakistan-based terrorist group Harkat-ul-Jihad-al-Islami to various media houses claiming responsibility for the explosion which left 13 dead.
Investigators had traced the e-mail to the Global Cyber cafe in Kishtwar.
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