Mannfred is pretty much the sole reason Nagash has been resurrected. Nagash is the most massive asshole you can possibly imagine, but he DOES reward those of his followers who work well and complete their objectives (just like he smacks down curse after curse on those that fail). Whilst Mannfred would be the youngest of his Lieutenants, he is likely very high ranking within the pecking order.
This would surely create tension with Vlad, who would have had to be ressurrected by Nagash, and without his ring would be quite handicapped in terms of power, a mere shadow of his former self whilst Mannfred outpowers even his Count Mannfred version (pending rules, but given the Mount alone it looks likely...).
Neferata would be further down the pecking order, because Nagash is not an idiot and highly cunning, so would be able to see Neferata's "bended knee" for what it was, simply to get back her own kingdom of Lahmia.
I have no idea what happened to Arkhan after Nagash's first (and second) fall. I know he's a special character in the TK army book but that doesn't really make sense, since TK hate Nagash, they'd surely hate his right hand man as well. Depends how they plan to fluff him. In the novelisation he comes across more as a ruthless but opportunistic slimeball.
