The group posted pictures of the funeral on its YouTube channel.
Omar al-Kayal and Ali Asfour tried to shelter from the air attack but the follow-up airstrike pursued by Russian air force claimed their lives.
On Thursday (June 27) Assad and Russian airstrikes hit the towns of al-Bara, Hazarin and Tarmala, without casualties reported.
The total Idlib death toll rose in Idlib to 7 as five civilians were killed in other towns on Wednesday.
After killing the two volunteers and the five civilians, airstrikes were conducted on civilian neighbourhoods in the cities of Kafr Sejneh and Saraqib.
On June 25 The United Nations humanitarian coordinator said that he had asked Russia to provide details on how it was using the location coordinates of hospitals in Syria following a string of attacks on health-care facilities.
Idlib, Hama northern countryside and Aleppo countryside are within the de-escalation zone reached by Russia and Turkey last September. Assad regime and its Russian allies have breached the deal, killing more than 505 civilians and injuring thousands since the 30th of April.