Personal dilemma... When is enough enough?

First off I'll say no, this isn't aimed at politics or anything of the sort.
Next I'll try and keep it short for a few reasons (And we had a rant yesterday).

I live with my cousin and his girlfriend. I have a for a year, and just a couple months ago they were given a beautiful little Japanese breed dog. Its a puppy, of course, and is not completely potty trained. Just before they got the dog they consulted me as to whether or not I minded because we do share a place together, and I was hesitant. Why? At the time they had two Bearded Dragons that they had had for a couple years, and after having moved in they began neglecting them. Well, about this time those lizards literally looked like they were about to do, so I told them straight up "No, I don't mind if you get the dog, but you need to take care of those lizards." And I was dead serious.

They sold the lizards to some nice fellow and got the dog - and back to my point... We've had the dog for a couple months now. The first wasn't too bad, the lack of potty training was tolerated, but I think the "discipline" has gone too far. I'm no animal rights fanatic, but I do feel there is a line between discipline and abuse. Rubbing its face in it and taking it to the door when it goes in the wrong place or giving it a light swat when it bites, to me, is adequate discipline, but as I said, I think its gone too far.

They leave the dog in its tiny ass kennel almost all day - even if they are home. And on top of that, they do what seems to me to be "sketch" to say the least. I keep to myself, but when the dog does something wrong and the girlfriend (Who does all of this) takes it into their bedroom and I hear yelping - I wonder. Today, however, almost threw me off my "keep to myself" perch.

I went to bed at about 3:00 AM and, seeing as how its the weekend and I'm in school/have a lot to get done, I was trying to get adequate sleep; however, I was woken up by muffled, scolding gestures, loud yelping, and noises one might associate with beating the shit out of something. I jumped out of bed, opened my door, and asked - politely - what the noises were. After a long pause, I hear the girlfriend, quietly mumble "nothing" and step out the front door. It had woken me up so abruptly I couldn't go back to sleep, so I grabbed a smoke and on the way out the door noticed a wet towel by the front door.

Not sure what the point of this is other than a rant and asking for others input, but I've reached my threshold with them (primarily her, if I were to make a rant why it would be a couple pages); and I'm torn because my cousin was the closest thing to a brother I had growing up, and I don't want to harm our relationship anymore than has been done over the past year of dealing with them.

~fumes~