TedStixon

Answer: Most likely his mom called them. She could sense something was wrong, and then the scene transitions, and the police are already there, so some time has passed. She probably went inside, found all the bodies, and called the police.

TedStixon

Answer: Michael is trying to show Laurie that they are siblings and that he (presumably) means her no harm. Since Laurie was a baby, she didn't mistreat him like everyone else does, so she seems to be the only person he is not driven to kill. (Similar to his mother, who treated him well.) However, Laurie doesn't understand and tries to kill him, causing him to then interpret her as an enemy.

TedStixon

Answer: To be fair, she also makes a snide comment about how the cute baby "couldn't possibly be related" to Michael, implying he's ugly. (At least in the unrated version, which is the most widely available version on home video. Not sure if this line is in the theatrical cut.) So she did also insult Michael. But the fact of the matter is Michael is psychotic, and felt compelled to kill her for one reason or another. Whether it be because she insulted him, because the picture of his sister set him off, or simply because he just wanted to murder her... he acted on his impulse to kill. I don't necessarily think there's always a rhyme or reason as to why he kills in the Rob Zombie films... he simply kills anyone who gets in his way or that he comes across.

TedStixon