<human>: Condense the text into a few key points

My older sister has been dating this guy on and off for a couple years. He is the worst fucking person I have ever met in my life. He has cheated on my sister numerous times, and every time, she kicks him out for a day or two, then takes him back. Not only that, but right now, one of his friends (an EX-CON) is living with them and it's driving me insane. But that's not the main reason I'm mad. I'm pissed because my sister's kids have to live with this shit.

My sister's children are from different dads. Miss (names changed, obviously) is 11, Dude is 8, and Lil Miss is about 2 or 3. They have seen my sister with a bunch of different boyfriend's and are basically the only reason I put up with my sister's crap. As kids, they should be worrying about kid stuff, but instead, they have to worry about when their food is going to run out and how the bills are going to get paid. And with this new boyfriend in the picture, things are worse than ever for them. He is one of those guys that basically says "Do whatever I tell you or else I'll beat the shit out of you." My sister has told me time and time again that she will never let someone besides her touch her kids, but I'm scared that something will happen.

I need advice on this situation. Nobody in my family knows what this guy did to get into prison, but they all want him and her boyfriend out of the picture. I'm not kidding when I say literally everybody in the family fucking hates him. But my sister will simply not take any of our advice.
<bot>: My sister's boyfriend is allowing an ex-convict around my nieces and nephew and nobody is doing a thing about it.