Complex sentence: It has been implied that either Rosanna or Tessa is likely to be a member of the Black Council, possibly both, although given Nicodemus' penchant for scheming, it cannot be entirely discounted that this is some sort of ruse.
Split into simpler sentences: It has been implied that either Rosanna or Tessa is likely to be a member of the Black Council, possibly both. Given Nicodemus' penchant for scheming, it cannot be entirely discounted that this is some sort of ruse.