Turn and get ready for one more charge. This one isn't too bad actually. Advance up the hill and get behind some hay. Pick off a few soldiers near the top and then look to the right. Your mission is to hit the small guard position behind the fence to the right. There should just be about 6 guys. Once they're dead, you should be able to get right next to the church. Kill a few men on the right side and watch for a moment. Dexter's group will advance on the church from the right and effectively crush the entire guard. Kill a few stragglers around the area. Then go through the church and make sure that it's cleared out. Also look around and see if you can find a Henry rifle. Fire at a few more of the Confederate soldiers to drive them off and secure the church. Dexter will give you the update when he sees you.

click to enlarge
This is a standard defense mission. You and a skeleton force of soldiers need to hold the church against a major counterattack. You'll drop whatever weapon you were holding and get a fully loaded shotgun to help out.
This is a simple concept that is quite difficult. You can't just hide in the church. They'll surround you and gun you down if you do that. You need to fire while moving quickly around the church. Step outside and watch the side by the forest. Take cover and use the Henry rifle for now. Pick off the wave of about 15 men. A second wave will hit the other side just as you finish up. Use the open door for cover and attack them as they set up.
Once this is done, a huge group will attack from the back side of the church. I suggest that you just whip out the shotgun and start firing into the crowd. Just circle around the building, watch your back, and fall back into the church if you need to heal. Some of it will just come down to luck though. If one Confederate manages to get behind you, then you are in a lot of trouble. They should eventually break.
Once you get the signal, just fall back to the marked exit.