QV estimates the property is worth $660,000 while homes.co.nz puts the value at $680,000.
Ewe's family believe the company took advantage of the elderly woman to secure a bargain and say there is no way Ewe gave informed consent.
The company has declined to comment, although Lee denies misleading Ewe and says the sale price was fair.
The family engaged Doug Cowan Barristers & Solicitors on Friday after being referred by the Mangere Community Law Centre. The firm immediately wrote to Auckland House Buyers' solicitors asking for the sale contracts to be cancelled.
It is understood Ewe, her family and their new lawyers will meet Lee and his legal representatives today to discuss the sale and make their demands.
"We've written giving notice that we're not going to proceed with the agreement," Ewe's lawyer Callum McLean told the Herald.
He declined to comment further pending the outcome of today's meeting.
Ewe was nearing the end of 12 rounds of chemotherapy when she responded to an unsolicited flyer in her letter box stating: "For a fair offer & no agent fees, call today."
She says Lee turned up at her home that afternoon and secured her signature in less than three hours, without her getting legal advice or discussing the sale with family.
"That's how friggin' dumb I am," Ewe said through tears last week.
"I'm so embarrassed by what I've done."
Consumer NZ chief Sue Chetwin said the case "smacks" of unfairness and Ewe may have grounds to overturn the contract "because she hasn't been properly advised".
Lee has said he didn't want to say anything "that can jeopardise my position".
But in a text message to Ewe last month, he defended the sale process.
"At the time of the meeting we were both very clear and i invited all your family members to sit in on our meeting as well. Given property needs to be modernized [sic] and there are not agent fees involved the price is a very fair offer."
Ewe's GP Mike Lovell-Smith said she was vulnerable at the time of the sale, having undergone chemo and stomach cancer surgery, and a recent CT scan identifying lung cancer.
"It would be easy for people to take advantage of her in her current poor health."
Auckland House Buyers and its offshoot Property Wise buy and sell homes in private transactions. Its salespeople are not subject to real estate industry code of conduct rules or regulations under the Real Estate Agents Act.
Auckland House Buyers' websites was deactivated after the Weekend Herald's story on Saturday, and Property Wise has dropped information on its team members and deleted links to online tutorial videos by Lee's colleague and Property Wise's advertised director, William Watson.
Labour's Housing spokesman Phil Twyford has labelled such companies the "real estate equivalent of clothing trucks and finance companies", calling for tougher regulations.
Consumer Affairs Minister Jacqui Dean told the Herald on Sunday she wanted to hear from anyone who felt they had been deceived during a private property transaction and would consider tougher rules if evidence of a wider problem emerged.
Ewe is unsure where she will go if forced to leave her house and may have to move in with grandchildren.
