The pair were released by manager Jay Saunders as the summer shake-up continues.
Okuonghae (pictured), who finished this season on-loan with National League South outfit Welling United, joined the club last February.
The former Colchester United skipper brought a wealth of experience during the run-in of the Stones’ first season in the National League.
He went on to make thirty-four league and cup appearances across the two campaigns.
Saunders told the club`s official website: “Mags has been first class throughout his time here. He came in around the time we went on that good run at the end of last season and was an experienced head that we needed in the back line.
“He was a pleasure to have around the club and we wish him all the best for the future.”
Osei made eleven appearances for the Stones after signing from Oldham Athletic in January.
He scored on his debut against Heybridge Swifts in the Buildbase FA Trophy and doubled his tally with a goal in the Kent Senior Cup semi-final.
Saunders said: “It was a big upheaval for Darius after leaving Oldham and fair play to him for moving away from family and friends to come down south and join us.
“He’s a great lad and I am sure a club closer to home will come in for him over the summer”.