(BENDY)
I personally think Bendy has a fear of death, which is only amplified by the fact he has the ink illness. He is also afraid of hurting others whom don't deserve to be harmed, such as Boris.

(BORIS)
Boris is afraid of falling in love. The main reason of this fear is bendy's ink illness, and their parents' deaths. Everytime he has felt 'love' for anyone, they either die or become extremely ill. He is also afraid of failure, mostly the failure of finding the pieces of the ink machine.

(CUPHEAD &MUGMAN)
The cup headed brothers are very protective of each other (although this is canon my reasons aren't).
Ever since they were little sippy cups, Cuphead has always been protective of his little brother, mugs, against the devil. The devil, along side their dad black hat and their uncle flug, has taken careful and kind care of the two when they were young, however as they got older the Devil tricked them into selling their souls. Mugman, though always cautious around the Devil anyhow, enjoyed being protected. Once the Devil got into Cups mind however Mugman broke into a panicked agreement, causing Cup to go all out.

(FELIX)
Felix is afraid of failure. He is also afraid of settling down with a lady. He has learned that failure on his adventures leads to death, feeding onto his fear of failure. He is afraid of settling down with a lady (having children with a lady moreover ) is because he is afraid she will force him to stop his adventures, thus forcing him to stop writing.