Can you get custody of your siblings and at what age?

Im 17 living with my boyfriend and my two babys at his parents so don't usually see my family but the problem started last year in feb. when my 19yr old brother ped away he was murdered in side a home full of prostitutes,drug addicts,etc We blame it on my mom cause she never wanted him in the house so my bro was homeless at that time now my mom felt she brought death to her son and then my dad went to jail he will be doing big time so she got depressed and stopped taking care of my siblings. My mom just couldnt handle it too much pressure and stressed she just stop living and few months after my brothers death she lost the house so she was livin in her car and abandoned my 13yr old brother and 12yr old sis. I would let my siblings stay over with me cause they told me they were tired of sleeping in the parks and at thier friends houses so i took em in with me but then my boyfriend's parents got tired of them cause they had caught my sister stealing from them so I had to tell my sis to leave it was painful cause my brother also followed her now I dont know where they at or how they are doing and just yesturday one of my lil brother's friend told me that my brother was in juvi I just dont want them ending up like my older brother Im scared dont want them in cps either nobody of my family members like my aunts and grandma want anything to do with us I went to see my mom she was druged she got worst she told me she didnt want nothing to do with us to leave her alone I told her I Want custody of my siblings but can I ? or what should i do?