If that rifle with that set of problems was brought to my shop I'd handle it in steps. BTW, I do have a Richland Wesson and recently had to remove the barrel because of a different problem. I was sweating bullets when I did it because, as I mentioned in an earlier post, the walls of the cast receiver are fairly thin and case hardened to boot. It's an invitation to a cracked or warped receiver. I don't recommend removing the barrel unless absolutely necessary. Here's what I suggest.
First, deal with the cross-threaded nipple. The threads in the receiver can be rethreaded to a larger size if necessary but first check to be sure it isn't just the nipple threads that are damaged. It's a lot easier to buy a new nipple than to recut the threads in the receiver. If you have never tapped (cut threads) then I can only say "be careful". Remember, the receiver is case hardened. Turning a tap by hand could result in a broken tap in the hole and you will have another problem to deal with. Also, you will need to use a "bottoming tap" not a "taper tap" because the hole for the nipple is shallow. Once done leave the nipple out for now.
Once the threads are taken care of you need to get that grease out. Remove the buttstock and forend wood. To remove the buttstock remove the screw that holds the trigger guard to it, no need to remove the trigger guard, then remove the buttplate. You will see the head of a long bolt that goes up through the stock and screws into the rear of the receiver. Use a large slot head screw driver to remove the bolt and the stock slides off to the rear. To remove the forend you remove the single screw that holds the forend cap in place and the forend is gently pulled down and forward to remove. Next get an old pot that is fairly deep. The deeper the better. Fill it 3/4 full with water and bring it to a boil. Best to do this outside if possible because this can get a little stinky and if you are married you may find yourself sleeping outside. That wouldn't be too bad in Texas right now but I hear it is still cold in Canada. While the water is heating remove the screws that hold the plate on the left side of the receiver and remove the plate. The internal parts won't fall out. Once the water is boiling stick the receiver and rear portion of the barrel down into the water. We want it to heat so that the grease gets thin and will flow. Put a wet fairly tight patch on a jag and try to pump water up and down the bore. If the grease got by the stuck piece of ramrod and patch, water should be able to do the same. You should see grease start to come out of the hole the nipple goes in. Keep pumping until all you see is water jetting out. If you are really lucky the stuck portion of rod and the patch might get sucked up toward the muzzle and come out as well. If the bore is blocked tightly enough that water can't get through then hold the muzzle end and swing the barrel like a baseball bat. Be careful because the barrel is hot and the grease will be too. Hopefully centrifugal force will force the grease out. It doesn't have to all come out but as much as possible would be nice. Once you have gotten as much grease out as possible, let the gun cool, lube the internal lockwork (that's why I had you remove the sideplate), and replace the sideplate. If the rod/patch didn't come out with the pumping go to the next step.
Run a rod down the bore to see where the obstruction is. Mark the rod with a pencil, withdraw, and hold along the outside of the barrel to get a visual. Then, with everything nice and dry, dribble 4fg powder into the hole the nipple goes into. It doesn't take much, about twice the amount used to prime the pan of a flintlock. Carefully install the nipple. Cap, point in a safe direction, and fire. Hopefully the rod/patch will be blown out. If not, run the rod you marked earlier back down the bore and see if the obstruction has moved. Remove the nipple, dribble in more powder, cap, and fire again. Check to see if the obstruction has moved. If it is stubbornly remaining where it started out then you are probably facing having to remove the barrel.
Before anyone has a heart attack about me advocating blowing the obstruction out even if there is a separation between powder and the obstruction, let me say that I've done this hundreds of times over the last 40 or so years and never had a gun blow up or a barrel bulged. The amount of powder used is just too small.
The rifle you have really was advanced for the time. Edwin Wesson designed it in the 1840's. He died in January of 1849 while in his late 30's. He trained two of his brothers as gunsmiths. One of them, Daniel, later formed a partnership with Horace Wesson in a company called Smith & Wesson.
Good luck! I hope this helps. If you were local I'd tell you to bring the darned thing over and we'd take care of it.
John