Rebel the Wolfgirl

I can at least suggest someone to replace Al. He might not be exactly the same, but you'd be surprised how flexible and universal he can be. If he can be a Jim Carey sound-alike, then he could easily be a Weird Al sound-alike: Rob Paulson! Great voice actor, years of experience. A second, similar choice would be Tom Kenny; he also has a lot of flexibility. He can do way more than just the Sponge Bob voice.

Ooh, I can definitely see either of them "voicing" Lettuce: he's very much a Chaotic Neutral trickster in the vein of Bugs Bunny...especially considering his archnemesis (for a loose definition of the word) is Jestia Spade - who I can only describe as a female Nolanverse Joker, which contrasts nicely with Lettuce's generally non-malicious character; he only causes havoc and mayhem in his wake unintentionally. Jestia, on the other hand, feeds on chaos and destruction - she's initially attracted to Lettuce (in both senses) due to her thinking he's a kindred spirit. Someone who does whatever they want to regardless of consequences (and in Jestia's case, threats to life).

Glad I could help. Also, I just thought of someone who might be a good replacement for John, if you're interested.