I remember reading that book last year, I really liked it . :)
Anyway, the difference between Tock and humbug, if I remember correctly, is: Tock is brave, loyal, and quite responsible, while humbug is selfish, talks nonstop and is very cowardly. Tock and Humbug have close to nothing in common other then one thing, that one thing being that they both become Milo's companions in the story and teach Milo valuable lessons about what to, and what not to do.
I hope this helps, if it does please let me know, and mark brainliest if you have the time. thank you :)