I totally agree with what Mrs. K and Aart said. There are always exceptions with any chicken behavior, but with my flock the immature chicks typically avoid the adults until they mature enough to force their way into the pecking order. With the pullets that's generally about the time they start to lay. Mature chickens outrank immature chickens in the pecking order. If an immature chicken invades the personal space of a mature chicken there is a real possibility of getting pecked. The chicks aren't stupid, they are real quick to learn to avoid that personal space so you wind up with two sub-flocks.
One way chickens evolved to live together in flocks is that when there is conflict the weaker runs away from the stronger. There can be some exceptions and there can be chasing, but typically if the weaker runs away and then avoids the stronger life is good, peace is restored. But this assumes they have enough room to run away and stay away. If they can't get away then the stronger thinks the other is still challenging it. That can be dangerous.
So how much room do you have? I'm not talking about square feet or square feet per chicken, I'm talking about can they run away and get away? You only have four total chickens, that often means space is limited. I'm encouraged that you at least have enough room to put a crate in there.
Room is not limited to coop size. Chickens don't understand the concept of coop space versus run space. If room is there and available they can use it so how you manage them plays a part. If they are locked in the coop section only then yes, coop is all that counts. If you can manage them so run space is also available your task just became a lot easier.
The quality of your room makes a difference. If you can add clutter so their line of sight is broken you just helped yourself. Clutter is something they can hide under, behind, or over. Having more than one feeding or watering station can help, especially if there is clutter between them. It is typical in my coop when I go down in the morning to open the pop door for the chicks to be on my 5' high roosts while the adults are on the coop floor. At night the adults slept on the roosts while the juveniles slept on the coop floor. They are avoiding the adults. Life is good.
My goal for integration is not that they all sit around the campfire eating s'mores and singing cumbaya. My goal is that no one gets injured. Nothing more complicated than that. All that one flock stuff comes when they are mature enough to handle it.
So what can you do? My suggestion is to release the two chicks when you can be around to observe. As I said, there are always exceptions. Sometimes with plenty of room there are problems. Sometimes even if they are shoehorned in there pretty tight it works out. Base what you do on what you see, not on what some stranger like me over the internet tells you that you might see. You never know what will actually happen, but two separate flocks until the juveniles mature is pretty common with my flock.
