Yeah, that sister thing is pretty weird. I'd be steering clear of that drama llama.
The animal thing. Hoy. Just make it absolutely clear if anyone asks that you're the one that called the cops on this person. Heck, bring it up to anyone you think would care before they hear it through a rumor mill or something. It's kinda stupid, but if you're the one who comes out and says that you're openly and actively against it, people are likely to see you as such, but if you've been keeping quiet about it and word gets out, people might (very minute chance) come to a misguided conclusion that you associate with those types of people on purpose.
The reason it's a minute chance is because humans are silly. We see things from our perspective and constantly worry about what other people think of us because we know everything about ourselves. On the flip side, think about how much time you spend personally judging other people. Chances are, not much time. Maybe an errant thought here and there. Most people are far too worried about their own self image and lives to bother putting much conscious effort into judging other people on a day to day basis.