Karmelo Anthony News Conference Delayed by Victim's Father's Appearance

10:38 AM PT -- Next Generation Action Network president Dominique Alexander began the press conference several minutes after police sorted out the issue ... and he kicked things by ripping Jeff Metcalf for appearing uninvited. He called the man's behavior "inappropriate," and "a disrespect to the dignity of his son."

Alexander then went on to blast media members for spreading falsehoods about the Anthonys in wake of their son's arrest -- appearing to take the biggest issue with the family's GiveSendGo funds, which he was adamant nobody had access to until Wednesday.

Karmelo's mom, Kayla Hayes, then addressed reporters ... and emotionally pleaded for the threats and harassment she and her family have received to stop.

Alexander ultimately wrapped up the event by insisting this will be their last press conference until a trial for Karmelo begins.

Karmelo Anthony's family was slated to address the teen's murder charge at a news conference roughly an hour ago -- but they put a pause on the proceedings ... as the father of the boy who Anthony allegedly killed unexpectedly showed up to the event.

The tense scene just unfolded minutes ago at Next Generation Action Network's headquarters in Dallas ... when Austin Metcalf's father, Jeff Metcalf, surprisingly appeared among media members just minutes before the Anthonys were about to speak.

Reportedly, NGAN officials -- who are helping represent Karmelo in his criminal case -- did not want to have the Metcalfs and Anthonys in the same room ... and asked Jeff to leave.

But, according to journalists on the scene, Jeff initially refused. NGAN then called Dallas PD to have him removed.

Seconds ago, a cop was seen speaking with Jeff ... and he left.

The Anthonys had vowed to "clear the record" at the newser regarding claims that had been made about Karmelo following allegations he stabbed Austin during a dispute at a high school track meet earlier this month.