Why is "Ille paterfamilias est" wrong?
It should be okay (in my opinion), please report it.
Shouldn't there be an ibi in the sentence or does Latin's ibi only denote position and not presence?
"Est" by itself can announce the existence of something, especially when it is positioned first. "Sunt" likewise can mean "there are".
"Ibi est paterfamilias" would mean "there's a paterfamilias there".