I agree with
@aart and
@Wyorp Rock. Don't throw the babies out with the bath water yet. At least not until you get a solid diagnosis of what is going on.
The wing paralysis and general paralysis can be signs of Marek's and Marek's can weaken the bird's immune system so they are more susceptible to disease but I agree with Wyorp Rock something about the birds with respiratory problems doesn't ring true to Marek's. I have Marek's in my flock and I haven't lost a single bird to respiratory problems similar to what your birds are experiencing. I have lost birds to respiratory and cardiac failure from probably tumors and Marek's and they act differently than you birds are acting. No discharge from mouth or eyes other than some mild bubbling from the mouth indicative of fluid in the heart and lungs but no crusting of eyes or nose.
Having Marek's in your flock need not be a death sentence to your birds. I was devastated when I figured out what was happening to my birds. I lost over 16 birds in a 40 bird flock since February but since then my census has increased to 60 thanks to prolific Old English Game Bantams. Yes, you are going to loose birds. Yes, your days exhibiting birds is over, but your surviving birds will be resistant to the disease and it's from those birds that you breed your flock from. Stay as far away from poultry shows as possible so you do not bring anything new in to infect your flock or carry anything in to birds being exhibited.
I only cull birds when they are exhibiting terminal symptoms of the disease and are suffering. Until then, my flock is closed. I breed from my own birds and only buy vaccinated chicks.
As for soil containment. Sorry, it probably isn't going to happen. You would have to scrape 6 or 7 inches of top soil off your entire property to be certain that you have eliminated the virus from your soil. But then, the virus can then travel in on the wind or on wild birds or from a neighbor who visits who is carrying the dander of infected birds on their shoes or clothing. Good biosecurity isn't a guarantee that you will not have Marek's introduced to your flock. At least it wasn't for me. Here in the US, the disease is so prevalent that avian vets consider all flocks to be exposed whether they are showing symptoms or not.
So please don't think the worst and even if your birds do have Marek's it is not a complete disaster. Yes, you will have birds die, but some will live and those birds are worth their weight in gold.
In the meantime do try to make contact with your farm vet and try to figure out what is going on with your flock. Sometimes, as mentioned the only way you can be sure of a diagnosis is to have a dead bird opened and labs done to pinpoint the cause of their death.
You've gotten good advice on general common sense care for your sick birds. I sincerely hope that you get to the bottom of what is wrong with your birds.
You may want to check out the Marek's Fax thread here on BYC. Lots of good info to be found there.