The Dewsbury-born siblings are now united at South Sydney, with three of them in the squad for Sunday's game against New Zealand Warriors, and McNamara admits it would be a marketing coup if they were to all play for England.
"It would be a marketing man's dream but players are picked on performance, not to make history," McNamara said. "Sam and George have been in tremendous form this season, Tom has only played two games but he's made tremendous progress and Luke hasn't played yet due to injury. But certainly if all four make the Souths team and they go on a Grand Final run, it would strengthen their case."
Sam, the first of the four brothers to join the Rabbitohs after being "courted" by Hollywood actor Russell Crowe in 2010, says the first step will be for all four to make the Souths team.
"The main thing is using our form at Souths," said Sam, who insists his decision to seek Australian citizenship will not affect his availability for England.
"We're all available at the moment. We're just hoping to continue our form and get a game together at Souths and see where that takes us."
Tom, who left Bradford at the end of last season to complete the Sydney-based quartet, has played in Souths' last two matches as a replacement for George following his suspension for a breach of club discipline.
George is expected to return for Sunday's game and acknowledges making the World Cup is firmly in his thoughts.
"I'm looking forward to getting back in the Souths team for now but, if I were to play in the World Cup, it would be a dream come true," he said.