A Nightrider is stronger than a Rook (~5.25).
A pair of Ferzes was indeed worth 3, as you indicate (2 x 1.35 + 0.3), so slightly less than a Knight (3.25). I never tried to measure the pair bonus; the Fairy-Max engine is not a very good tool for that, as there is no pair bonus in its evaluation. So it often needlessly trades a pair advantage away. I should really do a systematic study of pair bonuses one time with an engine that recognizes those. Lately I have started to suspect that pair bonuses have little to do with color binding, but are a consequence of the fact that the move patters of two unlike Bishops can have so many orthogonal contacts.
Wildebeest is more like 6.5-7. That is a lot of synergy, if N=3.25 and C=2.25. But the value of the Camel is much suppressed compared to other 8-target leapers because it is very easily lost in the end-game: chasing it away from the center brings it very close to the edge, where so many of its moves fall outside the board that it gets easily trapped. The Wildebeest no longer has that problem.
While some are just guesses and assumptions by me (marked with ?) others are basically factual, based on many computer games.(Credits to HGmuller for those)
Pawn:1
Knight:3.25
Bishop:3.25 (0.5 for pair)
Rook:5
Queen:9.5
Empress:9
Princess:8.75
Ferz:1.35(0.3 for pair) (?)
I'd say a pair of them (on opposite colors) are around the same value as a knight.
Wazir:1.125 (?)
Prince (non-royal king) :3 (?)
Knight rider:4 (?)
Wildebeast:5.75 (?)
Camel:2.25 (?)
Amazon:13.25 (?)
Jester (Can move like a wazir,3 times in one turn,basically wazir to the power of 3):8 (?)