A sneer grew on Severus' face as he read Bell's owl. So Greyback hadn't stopped his pursuit of Lupin and all that was associated with him. It was no great surprise and the rather slapdash manner of it was also expected. He considered the letter and his reply for a several minutes before picking up his quill.
Bell,
As I am unsure as to precisely what information you are after, I shall give you the generalities and if you require more specific answers, ask them.
Greyback and the wolves in his pack are insane. They retain their minds during the full moon though I do not know the precise process they have used to acheive this. Do not think of them as being human. They do not. Their behaviour will be as much wolf-like as human. The pack is paramount. Natasha Vladmyre is Greyback's mate, not his girlfriend, wife or partner.
Greyback is intensely loyal to Rodolphus Lestrange and to a slightly lesser extent, Bellatrix and Rabastan Lestrange. While he is the alpha male of his pack, he views Rodolphus as being his alpha. As long as Rodolphus stays loyal to Greyback, he will remain loyal to Rodolphus. Rodolphus knows this and makes sure nothing disrupts it.
As for what they will do to Nymphadora Lupin, it will be nothing pleasant. Greyback despises Lupin and having Lupin's mate in his hands will only spur him on.