The bodies of David Miller, 24, and 23-year-old Hannah Witheridge were discovered on a beach on the island of Koh Tao on Monday.
A spokesman for the Royal Thai Police said brothers Christopher and James Ware had been questioned about the deaths, along with 11 Burmese suspects.
None of those questioned are in custody, he said.
Police Colonel Kissana, deputy police spokesman, said: “We have spoken to two British men but they have not been detained. We cannot rule them out. They were close friends and knew all about the victims.
“We have got to do whatever it takes to obtain concrete evidence.”
Earlier police said “strong evidence” had led them to a number Burmese suspects after blood stains were found on some of their clothes.
The spokesman said DNA tests were being completed and the results would be available today.
He added that police found forensic evidence suggesting Witheridge might have been raped.
Officers were also looking at the possibility the two victims were having sex on the beach shortly before their deaths, considered a taboo in the Buddhist country, he said.
The two victims, discovered semi-naked, both suffered deep wounds to the head and face, police said.