Thanom Chansamut and Kalaya Thavor were among 92 Thais arrested in July last year in Kawthaung, opposite Ranong, for illegal entry and encroaching on a forest.
However, the pair faced additional charges and were found guilty of possessing illicit drugs and weapons.
The others were convicted of illegal entry and encroachment on a local forest and have since received pardons.
Somchai Chansamut, a relative of Thanom, Sunday pleaded with Thai authorities to find a channel to seek the release of the pair or a reduction in the jail term.
He said the families were afraid the case might have been “forgotten”.
Mr Somchai said the Burmese government is known to grant pardons to inmates at the end of the year.
“This could be a chance for the Thai government to seek a pardon,” he said.
Col Uthit Anantananont, member of a local Thai-Burmese border committee, said authorities had been working on the case. However, he said Burmese authorities showed no signs that leniency would be considered.
He said the chance of the pair being granted pardons was slim.