Mpengesi broke the news on the SABC radio station, Umhlobo Wenene on Sunday afternoon.
The Sea Robbers were expected to release at least one of their four top goalkeepers following the arrival of Wayne Sandilands from Mamelodi Sundowns earlier this week.
Mhlongo had been heavily linked with a move away from the Soweto giants for some time, and initial reports suggested that he could be going to SuperSport United provided Pirates sign Ronwen Williams.
Williams has since signed a five-year deal with Matsatsantsa, making it impossible for Pirates to lure him to Parktown.
Mhlongo's agent, Mike Makaab, distanced himself from the news, saying he knew nothing about his client's move to Chippa.
I'm not sure who's fooling who, but it sure is not me. Brighton has not signed for Chippa United.— Mike Makaab (@MikeMakaab) July 16, 2017
Okwuosa had also been expected to leave Pirates following a disastrous first six months at the club.
He was signed from the Chilli Boys during the January/February transfer window, but he could only manage a single appearance which came in the 6-0 loss to Sundowns earlier this year.
Meanwhile, Mark Mayambela is also reportedly on his way to the Port Elizabeth-based club together with Mahlatse Makhudubela from the Buccaneers.