Aik Non and Aik Ki were abducted by the TNLA in March for alleged connections to rival ethnic armed group RCSS/SSA.
Thousands of civilians remain displaced by the conflict between a DKBA splinter group and the joint Tatmadaw-Border Guard Force contingent in Karen State.
Some 420 men, women and children are camped in the town of Sechaung, while another 62 ethnic Khami people shelter in a monastery.
“In the past, such a memorial event would not be allowed,” said the assassinated KNU leader’s niece.
The UNFC says that by branding the Northern Alliance as ‘terrorists’, the Tatmadaw has derailed peace talks.
Six armed clashes have been reported between the KNU and NMSP since September.