I thought that tata was personal male, So twoj would be twoi ?
That would be just in case "tata" was in plural. In singular we don't distinguish between personal male and impersonal male.
Maybe "eats" too?
Yes, why not simply 'eats' ?
isn't Farther accepted instead of Dad ?
The equivalent of father is ojciec (more formal).
I should have known that but obviously didn't
But it is accepted. It just shouldn't be the main answer (it actually may still be somewhere).
In English, "Dad's" is often used for "Dad is".
"Your Dad's eating a sandwich" is correct, but it was marked wrong.
I DO know my English. (My Dad's taught me well.)