Bilal Nagi, 21, was given six months on top of a three-year sentence he is serving for unrelated firearms offences.
Khaled Nagi, 20, was given six months' periodic detention.
Both pleaded guilty to affray.
Fenech, 39, required plastic surgery after the attack - which left his jawbone exposed through the skin, outside a cafe in south Sydney last January.
The brothers were waiting at traffic lights outside the cafe.
"It is a concern to this court that these sorts of offences are becoming a fairly common occurrence," said Magistrate Leslie Brennan.
"It's probably something that happens in all communities in Sydney but it seems for reasons I can't fathom, young men of various persuasions drive around in cars and for little or no reason, take offence, quite often at pedestrians, and inflict sometimes serious injuries to them before driving off.
"This would be the third such offence I have dealt with this year and in each case the victims have been left in a pool of blood.
"The message does not seem to be reaching those it ought to be reaching."
