US President Donald Trump's two adult sons showed up to court wearing nearly identical navy blue suits on Thursday, as they testified back-to-back in the fraud lawsuit against their family's business empire.

Even Donald Jr and Eric Trump's ties, both a pale blue, seemed co-ordinated. Only their shirts differed: Donald Jr's a daring pale pink, Eric's a crisp, business-like white.

Well, not only their shirts.

The two brothers' testimonies were a study in contrasts. Their public personas are inextricably linked with their father's business and political ventures, but their temperaments and reputations could not have evolved more distinctly.

Donald Trump Jr, the eldest, attempted to carry over some of the bravado and humour he displayed on Wednesday into his second day on the stand.

He continued to deny knowledge or involvement in the accounting practices that had run afoul of the New York state attorney general - despite running the company and being a trustee of his father's revocable trust.

"Rinse and repeat," he replied after a repetitive series of questions from state's attorney Colleen Faherty.

He even appeared to flirt with the courtroom artists during a morning recess.

"Make me look sexy," he joked to one of them.

Over the last few years, Donald Trump Jr has moulded himself into a younger, slightly more polished version of his father, the former US president. He is best known as a top campaign surrogate, occasionally mimicking his father's cadences.

His statements outside the Manhattan court were a more refined version of Donald Trump Sr's "witch hunt" defence.

Watch: Why Trump’s kids are taking the stand... in 90 seconds

"Unfortunately, the attorney general has brought forth a case that is purely a political persecution," he told reporters.

Eric Trump, on the other hand, was more circumspect when he began giving evidence late on Thursday morning.

While his brother dominates the political realm, Eric Trump has become primarily associated with the family business.

There were no quips from the witness stand while Eric Trump occupied it. His questioning was far more tense than his brother's.

After initially denying he had knowledge of or involvement with the statements of financial condition - the balance sheets that the attorney general alleged were fraudulently inflated - Eric Trump found himself confronted with emails he had been sent that mentioned such documents.

The attorney general's office showed a 2013 email that an employee had sent to Eric Trump, writing that he needed information for statements of financial condition.

During one especially heated exchange, Andrew Amer, an attorney for the attorney general's office, grilled Eric Trump about his knowledge of his father's financial statements.

Growing agitated, Eric responded: "We're a major organisation, a massive real estate organisation - yes, I'm fairly sure I understand that we have financial statements. Absolutely."

He later added: "I had no involvement and never worked on my father's statement of financial condition."

Unlike his brother, Eric Trump did not schmooze with court staff during the breaks. Instead, he stood in front of the defence table, shifting his weight back and forth as he waited for the judge to return.

Despite their differences, the brothers' fates are intertwined.

They run their father's business empire together as executive vice-presidents of the Trump Organization.

Both are now named in the New York attorney general's lawsuit that claimed the business engaged in widespread fraud.

And both could potentially lose their ability to do business in New York if a judge rules against them.

The man they allegedly did this all for - Donald Trump - was absent from court on Thursday, despite several earlier appearances.

He did, however, post a message of support on his Truth Social account.

"So sad," he wrote, "to see my sons being PERSECUTED."