For the non-Australians, and even non-Queenslanders in here, Brisbane City Council is a bit unusual among Australian councils in that candidates stand under their party banner. In other councils they normally run as independents, even though much of the time they are actually a member of some party.
Our voting system is Instant Runoff Voting, which is what we also use federally and in state elections, but unlike those, in council elections, it is optional preferential. This fact has been key in helping the highly conservative LNP win a supermajority of seats in past elections, since moderate Labor and leftist Greens voters have not always preferenced each other enough to win seats that probably would have been won under compulsory preferential voting. The LNP, as a result, has 20 seats compared to 5 Labor and 1 Greens.
Despite this, there are reasons to suspect the OP is wrong in saying the Greens "have no hope of getting in". The LNP's campaign has shown quite clearly that they are very afraid of the Greens at this election. Usually the LNP's main target would be Labor, but at this election they've barely mentioned Labor.
Polling says the Greens may win 5 new seats, which if Labor doesn't pick up any new seats would put them in as the official Opposition. If Labor does perform well, they need to pick up just 3 seats for a Labor–Greens coalition Council to be formed, or just 2 with support of independent Cr Johnston, assuming the Greens pick up all 5 of those expected seats.
The most likely outcome is, sadly, that the LNP wins and we get more useless carbrained nonsense. But "no hope" couldn't be much further from the truth for done genuine progressive change.