Khan had been informed about the stance of the banned Tehrik-e-Taliban Pakistan and he "had showed his willingness to play his role to bring peace back to the country", sources close to the Taliban were quoted as saying by The Frontier Post daily.
Fahim, a top leader of the ruling Pakistan People's Party and the Commerce Minister, was in the Taliban's "good books" and it was likely that he would be included in the list of the guarantors, the report said.
Unnamed members of the grand jirga too said Khan and Fahim could be included in the list of guarantors.
The Taliban had originally named PML-N chief Nawaz Sharif, Maulana Fazlur Rehman and Jamaat-e-Islami chief Munawar Hasan as possible guarantors for the peace talks.
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The six-member committee would work as mediators between the grand jirga and the Taliban, the sources said.
An unnamed grand jirga member said the process of talks was underway and "positive progress" was expected soon.
The grand jirga has met with the "high ups" of the Taliban and they had expressed satisfaction at recent developments, the member said without giving details.
Tehrik-e-Taliban Pakistan chief Hakimullah and other commanders have made offers of talks to the government.
The Taliban have refused to disarm ahead of the talks.
The government has been insisting that the militants should declare a ceasefire and give up violence before talks.