If we removed all his dialogue, Jonathan would be tolerable, besides his silly boots with door knockers on them. Charlotte's design is a too school girl generic for me though.
In gameplay, Jonathan was awesome with his variety of weapons though most were dull. Charlotte's spells were good. But with both combined, it wasn't executed that well. The two character set up made it feel clunky in a way. It would have been better if there was just a single character. The times where two were actually needed like with pushing and jumping on each other also were rare. Needing to push with the two of them out also just seems unnecessary.
They could have been good, but the game was executed in a way full of silliness and redundancy.