Plange, 19, and O’Brien, 21, will spend the rest of 2022/23 at the Edmond Machtens stadium as Molenbeek look to gain promotion from the Belgian First Division B.
Centre-back O’Brien initially joined Palace on loan from Cork City in February 2021, before making the move to south London permanent in July 2021. His performances for Paddy McCarthy’s Under-23s in 2021/22 earned him a contract extension and half-season loan to Swindon Town midway through the campaign.
Forward Plange signed in January 2022 from Derby County. He penned a three-and-a-half-year deal and was immediately loaned back to Derby for the remainder of the 21/22 season. He notched four goals and two assists in 26 appearances for the Rams in 21/22.
Commenting on the move, Plange said: “This is an exciting opportunity for Jake and me. Personally, I’m looking forward to it. It will be a completely different challenge to play in a new country and in a new league.
“I hope to learn a lot at Molenbeek and help them achieve their goal of promotion to the top-flight.”
O'Brien added: “Playing in Belgium will be a new challenge, but I’m really up for it.
“It might be tricky at first, but I will work hard to establish myself in the Molenbeek squad and press on from here.”