I heard my mom say this, "a fèk gade yo si yo pa kwè ou pa ka travay." is 'a fèk gade yo' equivalent to 'ki mele yo'? I have heard her say this expression a lot but it's the first time I'm actually aware of it.

There's a little difference.

afè k gade w (or zafè ki gade ou) see link to other ways to say this in Creole
business which concerns you (lit)
It's your own business
It's on your head
It's your choice

afè k gade yo (or afè ki gade yo)
affair which regards them.
It's their business
It's their choice.

See other links: That's my business
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Ki mele yo ( or Ki te mele yo)
What do they care?

See link about Who cares?  for more ways to say this.

Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words