Are these grounds for child neglect and can I have sole custody of our twins?

I am the residential parent of my children for school purposes according to the shared parenting agreement I have with my ex-wife, giving her the standard order of visitation. On the weekends, she has my twins. She sends them to school in dirty clothes, including dirty panties and socks. My twins are 6 years old. They ask their mother to wash their clothes and she refuses, stating that she doesn't have to wash them. I even send with them clean underclothes, only to find out that their mother didn't put them in the clean things I send. Their mother also ignores their basics needs for nutrition by refusing to give them the vitamins I sent, and purposely feeding them junk food for breakfast, lunch and dinner. Examples of this are chocolate waffles with peanut butter, Nutella, and syrup for breakfast, hot dogs for lunch, and letting them eat cheese balls and lunch meat for dinner. The twins have reported this to me after every visit, and these things have been going on for more than three months. Her boyfriend also exposes them to excessive alcohol consumption. She also sends the children away to her parents every weekend she has them to go to bars, parties, and concert events. Her sister is a known drug user as well as her boyfriend, who the girls tell me have been in jail twice in the past few months. Their mother also takes away their "security blankets" as punishment and refuses to give them back because one twin brought a doll from their mother's house to mine. Another incident, on their birthday, one twin got a gift that cost $150 and when the other asked why she only received Legos their mother replied "I couldn't get you anything nice because your sister's gift was so expensive". She was so distraught, and she tells me that her mother favors her sister more so than she, because she is always receiving nice things, while my other daughter doesn't get anything. Are these grounds for willful neglect of the children's needs? What can I do?