analog

With all due respect, why is he walking around on two not-broken legs? Or at least without several large, baseball bat-shaped bruises?*

It's not your fault that he hits your mom. It's not your job to help him patch things up with her.

But you don't seem all that phased by him hitting her- and you don't seem to be helping her get away from that abuse.

There is no "only" x number of times he hit her. Don't rationalize it because he's your dad, don't rationalize it because of "hard times", and don't enable him by pretending like it's not a problem- because if you don't seem all that concerned to us, and you're just asking for advice on whether or not to help get them back together, you're obviously not that concerned. And you should be. A lot.

Think of your mother, man. Think of your little sister. While a divorce would not be "optimal", it's better than continued abuse. Or are you waiting until your little sister is old enough to get hit, too? You're a person of age to do something- whatever it is you can. So help your mom and sister in whatever way you can. This does not include getting them back together with the repeat abuser.

/tough love

*I am not actually suggesting or advocating violence. /covering my ass