Help please, my nieces are raising themselves when they are with their mother, any advice on what we can do?

Their ages range from 8 to 14. She has custody, works late nights and sometimes stays after hours at the bar she works in, not coming home until 2am-4am. The girls father would keep them during those hours but to prove her point that SHE has custody, she would rather they stay alone at her place (rather than with their father). She has had numerous boyfriends come in and live after only a week or two of dating them. These strange men sleeping over even when the girls are present. The father pays child support although, at one point in the past year he had them 65% of the time. There's so much, as an outsider, that I see wrong in this picture. These are all impressionable young ladies, will the vicious cycle continue with the choices she makes now, influencing choices they make as adults. But anyway, getting off track....what, if any, legal angles could someone suggest their father take to do something about them living alone and raising themselves while Mommy is working and partying until wee hours of the night? There was even one morning, where one of the girls wasn't feeling well, and she couldn't get her mother up to take care of her, she was sleeping in bed with her new boyfriend she's dated for 4 weeks. So my niece called me and her Dad for suggestions and told her she probably shouldn't go to school. She informed us that her mother doesn't get up until 5 minutes before they have to leave for school. She woke up an hour late that morning and none of the girls made it to school...she did on the other hand take them out later that afternoon to get pedicures. I don't know, maybe there's nothing to do here, I just needed to ask. Thank you for any input, whether it be positive or negative.