In a recent interview with Ari Millen, it's discussed that all the Castor clones were raised self aware:
Unlike the Leda clones, the Castor brothers were raised self-aware, which attributes to their "very close-knit wolf pack of a military upbringing," according to Millen. "Just like any sets of brothers, there's a real closeness. They like taking the piss out of each other. They can be vicious. There's also a lot of love there."
And that includes Mark:
That said, there will be conflict because, after all, they are brothers. The obvious answer is that it will involve Mark. "He has his own idea of who he wants to be and where he sees himself going, and his brothers and Project Castor are gunning for him. They're not going to let him go without a fight," he said.