It might make sense for Malcolm/Denise to decide in advance to take Mike/Lisa to cement the relationship and keep them from strategizing with Abi and Carter. Just spec. It's good spec. Taking each other for reward would only risk the others getting a chance to talk without one of them around. The smart decision for them would be to have one on the reward and one at camp so that they're in the loop with the goings-on at both places.
Malcolm would make that sort of decision. He was crafty when he squelched strategic talk after he, Carter, Pete, and Abi won RC.
That also makes me wonder if the secret meeting is between Denise, Abi, and Carter to figure out a way to flush out Malcolm's idol. Denise was targeted during the last TC instead of Malcolm because of that idol, so she may want to help flush it out so that there's less of a target on her own back.