Lundy called the visit from the prostitute "a cashie" and Andrea Lundy remembered the brothers joking about the scenario.
"Craig said 'I suppose that's your alibi'," she told the jury.
"[Mark] made a joking sort of statement, saying 'yeah, I finished with her and drove back to Palmerston North'. It was in a sarcastic tone."
The issue of the couple's physical relationship was also raised "spontaneously" by the defendant during the lunch.
"He mentioned that once they found out they couldn't have children, Christine went off sex and it was up to three months without having sex," his brother said.
On the same day, Lundy informed his brother he had "bumped up" his and his wife's life insurance policy from $200,000 to $500,000 in the weeks before the deaths.
He explicitly said it was not a "motive" for murder and his lawyer David Hislop, QC, suggested it was to cover the liability of their new Hawkes Bay winery venture.
Witnesses this morning also gave evidence of the severe financial pressure Christine Lundy felt at the time of her death.
Her sister-in-law Maria Norrelle said the defendant had been trying to secure investment in the vineyard but people - including an uncle in Queensland - had pulled out.
"The last time I remember it being discussed was late at night. Mark mentioned that Christine wasn't sleeping well but he wasn't worried about it," Ms Norrelle said.
"He used the word bankrupt."
She also said Lundy's wife wanted to "change their lifestyle".
"She was concerned about the cost of partying and the influence it would have on Amber. She had said she wanted Mark to give up drinking for three months to see if he could."
Crown and defence will argue legal matters for the rest of the day, which cannot be reported.
No more witnesses will be called today.
The trial before Justice Simon France is expected to continue for another two months.
Key points
* Lundy joked with his brother Craig Lundy, four days after the deaths of his wife and daughter, about using a prostitute as an "alibi"
* Lundy told his brother he had used prostitutes on four previous occasions and his wife had not had sex with him for three months
* Christine Lundy was concerned about the financial pressure placed on them by the Hawkes Bay winery venture and was not sleeping
* Lundy mentioned bankruptcy in the weeks leading up to the alleged double murder
* Christine Lundy was concerned about her husband's drinking habits and wanted to "change their lifestyle"