I really don't understand my step sister. This is kinda Long so pay close attention please.

She's been in a long relationship with this guy that lives in Arizona. They have 2 kids togther so she lives in Arizona with him. They're in dysfunctional relationship. Which I don't really care for cause it's not really my business and I'm not getting into it when she's obviously is going to stay with him. I still respect him as a person but I don't like him if that makes sense.

Anyways my step sister comes to California maybe once or twice out of the whole year. And she stays with me and my family for a week or 2 the longest. Whenever she comes to visit me and my family her and her bf are on bad terms. Always. She's constantly crying ALWWWWWWWAYS angry she brings her kids to visit as well (my niece and nephew) but once she's crying and angry she doesn't pay no attention to her kids she doesn't watch her kids for shit. She ditches my niece and nephew and goes and gets high with her male friends. And she'll be gone for hours. I feel me and my 12 year old sister become parents to her kids once she's gone. I watch my nephew (he's 2) and she watches my niece (she's 3). The poop the pee making them something to eat I do all that she just plays with them. While we both do all that my step sister still is no where to be found. And when she is here me and my little sister are Still them taking care of them making sure there fed and clean. While my step sister is on her phone high not giving 2 fucks.

Well today i wake up and nobody is here but the kids. My niece woke me up crying saying "where's mommy" I got up right away searched the whole house AND OUTSIDE. She doesn't have a phone i don't know who she is with I don't know any of her friends and there numbers. So just to get my nieces mind about where her mom is, I woke up my nephew made them some breakfast took them both a shower got them dressed and we walked to the park. WELL WHAT DO U KNOW! I see my step sister at the park smoking up a storm with 3 guys out in the open. My niece saw her right away and shouts "mommy" with the biggest smile on her face. I got so pissed I took them back home. I don't want my nephew and my niece to see there mom smoking weed with 3 guys like that. Especially since she DICTHED THEM AGAIN for weed and guys.

So I called my bf told him everything and asked him if he can come over to help me watch them. He agreed. My bf brought his Playstation playing video games trying to teach my nephew how to play battle field (it was pretty cute actually). My sister shows up an hour after my bf came. She's all thanking me for taking care of her kids. I ignored her thank u and told her "since ur home now watch ur kids Ariella was crying asking for u she misses you so spend some quality time with them I made them food took them baths so ur set". She only played with them for 15 minutes and she falls asleep! I woke her ass up right away I splashed cold water in her face. Told her I was getting ready to leave and for her to stay up to watch her kids do something with them u know.

My bf was packing up his Playstation when he was done he sat on the couch waiting for me to finish getting ready. When I was done I sat on the couch next to him to put my shoes on. My step sister bends over right in front of his face ! She laughed she turned around where she's facing him this time and she bends over again and this time her boobs pop out. Not to the point where her nipples came out but it was alot to see. She's a size DDs. My bf got up so fast and told her she's shouldn't be disrespecting me like that and her man. He told her "after all the shit that she just did for you this is your way of thanking her, bending over like that in front of me have some damn respect for yourself stop making yourself look like a fool"

I'm not jealous of her I feel as if I'm way prettier than her. But my point is for her having such a bad relationship with the guy she's with do u guys think she's looking for attention from other guys? Her bf isn't a good father or a good provider he isnr faithful either. My bf is a good provider and faithful. My mom said she thinks my step sister can be jealous of me because me and my bf are always on good terms he doesn't cheat on me he has a job (he's a manager). My mom thinks everything that my bf has my step sister wants it. But she knows she can't have it that's why she bent over and laughed at me cause she knew my reaction when she did that. She knew I was some what jealous. I have a nice body myself but when I go Visit them in Arizona I make sure my shit is covered. I don't want my step sister to think she has competition with me or i want her man you know. So I just don't get it.. she's always smoking with multiple guys, she bends over in front of my bf twice and she looked dead at him when her boobs popped out thinking she'll get a fat smile on his face while she's smiling at him. Part of me just doesn't trust her. What do u guys think? Besides that she needs to step up and be a better mom

Update: I had a talk with her about the kids and that ditching them like this doing what she's doing she can lose my niece and nephew.. and I don't want them to go through this situation.. what I should I do or talk to about her problems and the kids?? Or there's nothing really I can do.. I'm 22 any advice??