Sriram Parameswaran, whose wife Sruthi Chandrasekaran is missing, issued an emotional plea to Prime Minister Anthony Albanese on Wednesday, as families ask for financial support and visa assistance.
Among a string of concerns, relatives said despite assurances Centrelink would contact them to discuss options, it has not done so.
"We definitely want to meet the prime minister, who can listen to us, who will be able to understand what our grief is ... he is the only person here who can now bring all departments together to help us," Mr Parameswaran said.
"I am not able to answer my boys' questions. They still don't know. They are still hoping that mum is going to come back, right? So we need an answer," he said.
Mr Parameswaran also detailed visa issues for multiple families including his parents, who he brought from India to help look after his two young sons.
He told AAP their visa will expire in March and the uncertainty of not knowing whether they will be able to remain in the country was troubling.
"When my wife is not there, the only person he trusts is my mum," Mr Parameswaran said of his two-year-old son's bond with his grandmother.
Speaking in Sydney, family members of several Australians who have been missing since August 26 described the community formed in the aftermath of disaster.
"We try to ... share our grief. We also have a WhatsApp group created with all the family members, so even if one person comes to know some information, we immediately put it in that group so everyone is made aware," Mr Parameswaran said.
"It's like we've become a very big family all together, but we all need an answer. That's what we are praying for, and we are waiting for."
Vaishnavi Kowshikan, whose sister Shylaja Muralitharan is missing alongside her husband and two sons, said time had stood still for families affected by the disaster.
"We don't even know where this time has gone," she said of the month since the floods.
Ms Kowshikan also described seeking answers from the Australian government about the whereabouts of her relatives, particularly nephews Ashwin, 14, and Aarush, 11.
In the event her nephews had been separated from their parents, she asked the government whether they might be in a children's home or rescue camp.
While the government told her no foreign nationals had been found in either, she expressed concern that they might be unable to identify themselves.
"Ashwin and Aarush are very young ... considering the shock they may have gone through, we're so concerned and worried. Can they speak? Can they identify themselves?" she said.
"They are our family, but it's not an impact on just my family of four. We're all in this together. We're all experiencing the same thing, so we're really reaching out to the Australian government. That's our final hope and final plea."
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