How can I get custody of 2 kids.?

ok i'm 19 I have a part time job and fixing to move to full time I have a small apartment 2 bedroom. I wnat to get full custody of my little bro and sis ages 12 and 10. how do I go about it their father is a drunkk facing murder charges for shooting the man his wife was sleeping with. Their mom is a druggy and has a rap sheet that goes on forever. what do I do.