If they were my Remington 1858's, the first thing I would do would be to place the hammer at half cock.
Then I would rotate the cylinder with my fingers. It should move freely in one direction and not at all in the opposite direction.
If there was some "drag" that caused the cylinder to not turn freely I would remove the cylinder from the gun and give the cylinder pin and the hole in the cylinder a good oiling. I would also try seeing how freely the cylinder rotates on the pin. It should spin freely.
While I had the cylinder out of the gun I would check the hammer and cylinder hand action by cocking the hammer and, with my thumb on the hammer spur, pulling the trigger to drop it.
I should be able to easily cock the hammer to full cock without any drag at all other than the force created by the hammer mainspring.
If there is a noticeable drag on the hammer I would try putting some oil into the joint between the hammer and the frame. If it didn't, I would put the gun back together and get ahold of the seller and tell him I the gun has problems and I want to return it.
For those wondering how to take the cylinder out of a Remington, this is how I do it. (My Remington's were stolen so I'm going by memory.)
The first thing to do is to unlatch the loading lever and lower it all the way down. Then, try to pull it out of the frame. It should not move forward.
There is a "screw" on the left side of the frame where the cylinder pin passes thru the front of the frame. It really isn't a regular screw. It is a special screw with a clearance cut in its body. With the screw in one position, the cut does not line up with the cylinder pin. This keeps the pin from coming out of the frame.
Rotating the "screw" 180 degrees turns the clearance cut so it lines up with the cylinder pin which then can be pulled out of the gun, releasing the cylinder.
With the loading lever and the attached cylinder pin out of the frame, rotating the cylinder clockwise (aft looking forward) should allow the cylinder to rotate out of the frame.
When putting the gun back together, place the cylinder in the frame opening by rotating it clockwise and pushing it in. Rotating the cylinder while you do this will push the cylinder hand back into its slot at the rear of the frame opening. If you try to put the cylinder in without rotating it, the cylinder hand will be in the way and it will prevent the cylinder from going all the way in.
With the cylinder back in the frame, put the cylinder pin back thru the hole in the front of the frame and thru the hole in the cylinder.
Once it is in place, turn the cylinder pin retaining "screw" 180 degrees to lock it in place, bring the loading lever back up and latch it and, your done.
Like the others said, if these things don't fix the problem, send the guns back.