I want to call animal cruelty

So my sister lives in a duplex and just in April a family of 5 moved in. They have a grown pit bull and a new pitbull puppy. I've never seen the grown one because they keep it inside most of the time and I've seen the puppy twice. They keep them in the garage all day when they're gone and there's NO ventilation in those garages and we've been having 90° weather here!! That's so cruel! Also, when you walk by the garage the grown pitbull gets really angry and viciously barks. We hear the dad beating the dogs also and they wine in pain.. this is a duplex so we hear that. Neighbors also looked them up and the dudes a dog fighter and had been in trouble for it before and I think that's why his grown dog is so mean because I've never met a mean pitbull to be honest and I just have a feeling that sweet puppy of his is being trained to fight. The dads usually home all day and leaves with both dogs around midnight. There's TONS of kids on that play over at my sisters duplex and if that grown dog got out.... that would be a scary thing. I also fear for the safety of his own kids who are very sweet btw. I know I'm going to report it but this is where I need help. I'm scared it will fall back on my sister even though I'm gonna do it anonymously. I'm really not trying to be judgey but the dad has other charges that are worrisome I guess you would say and I'd hate to judge someone by this but I wouldn't want him to get mad at my sister who has 3 kids.. they've always been nice to us and one of their kids is even dating my niece (they're 12) but ugh I just don't want them thinking it's my sister. Should I call? They abuse those dogs.. we can hear the dad abusing them. Leaves them in a hot garage. And I'm positive he uses them as fighting dogs... what should I do? I'm not sure if the grown dog can be saved but if we get them out of there I think the puppy would have a good chance of being a sweet dog since she's only 4-6 months old.