Hen With (Most Likely) Coryza

So two weeks ago, I ended up having to put my dwarf rooster down.

I never actually figured out what he had but it was an awful sight to see. After some research, it seemed a lot like Newcastle's Disease with his last few days. The weird thing is that my two other hens are perfectly fine (as far as I can tell.)

So.
One of my hens had this horrible, horrible smell when I bought her. At first I thought it was because of where I got her. It's literally been two months and she still has this foul smell -she's active and eating. Although I have noticed her growth is severely stunted...
(I can't help but find her extremely cute but I'm really concerned -she's the size of a twelve week-old hen.)

All three of my chickens didn't respond to the Duramycin10 I was giving them...
So my question -what medicine should I try now?

Online and from previous responses, Coryza or MG were the only disease I found that had stunted growth and smelly symptoms.
(Those are the only two symptoms she has -the other shows none which makes me think she's also a carrier.)

This smell NEEDS to go away!

Also, what's the difference between MG and Coryza..? I'm new to this, sorry.

Last -how would I go about getting more chickens if I ever wanted to? Or if I even can?
Despite the circumstances, I'll keep them anyway. They're more of pets than anything.

Thanks!