Maranoa is an outback electorate pollsters bill as the most opposed to marriage equality but even here a yes or no question is not quite that simple

“I’m 50-50, sitting on the fence – on barbed wire, you might say.”

The undecided man in his 70s, poring over betting slips with his wife at the local club in the Queensland town of Warwick, says he is not much bothered by same-sex marriage, since it doesn’t affect him.

“You’re going to have to make up your mind,” his wife reminds him sharply.

The nationwide postal survey forms that could decide whether the Australian parliament legalises same-sex marriage are already in the mail, and she declares her vote will be a resounding “no”, adding: “The Bible says it’s wrong and that’s all there is to it.”

The former colonial frontier town of 15,000 is the biggest in Maranoa, a sprawling outback federal electorate three times the size of the UK, and thought to be the country’s last main bastion of opposition to same-sex marriage.

But even in Warwick, couples and families are divided by the government’s move to put same-sex marriage to a survey, before deciding whether to follow an array of other liberal democracies and legalise it.

Facebook Twitter Pinterest The Australian marriage law postal survey forms are being sent out to households across Australia. Photograph: Cameron Spencer/Getty Images

The wife at the club confides their son is gay and the question of marriage equality has been the cause of “a lot of argument between us, and I think it would be for a lot of people”.

Last year, Maranoa was the only electorate in the country to oppose same-sex marriage outright, according to analysis of voter surveys. That puts it out of step with the rest of Australia, if that analysis and an array of opinion polls hold water.

As the campaign enters its second week, signs the yes case has the upper hand are balanced by uncertainty about whether a silent majority – less politically engaged and tending to not to be reflected in opinion polls – will produce a different result.

Some opponents have resorted to homophobic propaganda through unofficial leaflets and posters. Contrary to one Christian lobbyist’s claim the no side faced a “David and Goliath” contest, the official no campaign has so far outspent marriage equality supporters five to one on TV advertising. That is a space to watch, after Qantas airline boss Alan Joyce, an Irish-born gay man, last week personally donated $1m to the yes campaign.

Facebook Twitter Pinterest A supporter waves a rainbow flag at a marriage equality rally. Photograph: Morgan Sette/AAP

Leading parliamentarians, including the prime minister, Malcolm Turnbull and the opposition leader, Bill Shorten, support marriage equality. Vocal opponents include Turnbull’s predecessors, Tony Abbott and John Howard, who have linked the issue to a broader culture war and a secular progressive attack on churches.

The conservative Christian senator Corey Bernardi launched the official no campaign in Sydney on Saturday with the declaration “we’re under assault because we’re on the right side of legal and moral history”.

Play Video 1:56 Freedom of speech under attack by same-sex marriage, Bernardi warns – video

Back at the club in Warwick, a retired pilot tells the Guardian gay marriage is an unfathomable development to a generation that remembers when “homosexuality was something you could be prosecuted for”.

It was in 1989 in Roma, another Maranoa town, that the last charges were laid under Queensland’s homosexuality laws. They came in the dying days of rule by the conservative rural National party, which had governed for decades under Joh Bjelke-Petersen, a Lutheran preacher’s son who reportedly told his health minister Aids was God’s punishment for Aboriginal people.

Why Brexit and Trump make me nervous about the marriage equality vote | Brigid Delaney's diary Read more

But even in Joh country, times change.

In his home town of Kingaroy, the high school has backed its first openly transgender students.

Gavin Walker, 16, was born Gabrielle, and harassed in year 8 over a same-sex relationship before his transition. But when he became Gavin the “whole school was exceptionally supportive and the transition went fairly seamlessly”, his mother Sandy says.

Facebook Twitter Pinterest Gavin Walker (far right) is the first openly transgender student at Kingaroy high school. Pictured with (from left) his sister Xanthe and his brother, Matt, who is also transgender.

“I think the whole newness of the same-sex thing had kind of rubbed off by then, so it was just, ‘oh, OK, cool’,” she says. Gavin has an 18-year-old transgender sibling who was born Megan and is now Matt. Gavin “carved out the way” for his older brother and two other Kingaroy teens since to make the transition, Sandy says.

In Roma, a town of about 7,000, public servant Mitchell Greig says he is more comfortable being openly gay there than in Brisbane and Melbourne, where showing affection was sometimes an invitation for abuse.

Out here it’s never been an issue. I had a partner for the first two years and that was never a drama Mitchell Greig, Roma resident

“I’ve been out here for six years and I’ve lived in Melbourne and Brisbane and you could never go to a normal club and be yourself without any dramas,” he said. “Out here it’s never been an issue. I had a partner for the first two years and that was never a drama.”

But neither the yes nor no campaigns have had any visibility in Roma, Greig says.

Likewise in places deep in the outback like Charleville, according to local mayor Annie Liston. Liston says she will vote yes as “I’m supporting whatever makes people happy”. “I’m not against, I don’t give it thought, same-sex marriage doesn’t make any difference to me whatsoever.”

Benjamin Wilson, who came to Warwick five years ago with his wife, Mandy, says the issue of same-sex marriage is not being talked about much.

“We did have a guy putting leaflets in our letterbox the other day from the no campaign – the Coalition for Marriage, I think,” he says. “He believes that if the change in law goes ahead, parents are going to lose their right to decide if their children are allowed sex changes or not and he believes that homosexuality is against God.

“I just handed them back to him. I don’t think anyone has a right to tell people who they can and can’t marry.”

Facebook Twitter Pinterest Ricky Masculino, who settled in Warwick seven years ago from the Philippines. Photograph: Joshua Robertson/The Guardian

In Maranoa, as elsewhere, even some Christian couples are divided on legalising same-sex marriage.

Ricky and Nora Masculino, who came from the Philippines to settle in Warwick seven years ago, are Seventh Day Adventists. Nora says she opposes same-sex marriage “because we’re Christians, so we’re following what God has ordained, what’s in the Bible”.

But Ricky looks beyond religion. “As a Christian, I would definitely say no – when we’re talking about Christians,” he says. But he agreed with legalising same-sex marriage outside his church. “We came from the Philippines and the yes [vote] wouldn’t win in our country. But we’re here in Australia, and other kinds of country like the USA, the United Kingdom, same-sex marriage is – they’re talking about respecting others’ beliefs and decisions and hearts.”

Facebook Twitter Pinterest Maranoa MP David Littleproud. Photograph: Mike Bowers/The Guardian

The MP for Maranoa, David Littleproud, is not campaigning one way or the other, and will back the majority view in his electorate.

If the yes case wins, Littleproud says the legislation will be passed by Christmas and his electorate will “get on with their lives”.

“They’ll be worried about when it’s going to rain, what they’re going to get for their commodity prices, how they’re going to pay for their electricity bills,” he says.

Littleproud says he resents attempts to portray his electorate as the last holdout of bigotry. “Because we live in small communities, we are more tolerant of variances in views and I think we are a shining light on how this whole debate can be done in such a respectful manner.”