First of all well done in taking care of your niece and nephew. When you say the children are with you on a voluntary basis is this with just the agreement of social services or was it taken to family court and an uncontested residency order granted ? If the mother makes an effort to clean up her act the childrfen will not be returned to her without an in depth investigation into her present way of life. They only way you can help the children at the moment is to give then love and a stable life. You could go for special guardianship via the courts but it is early days in the situation but you could talk to Child Protection letting them know you have this solution in mind. Any evidence you have that the mother is continuing to present herself in an intoxicated manner should be gathered and presented to child protection, sneeky but you are only trying to protect the children. Finally, family court judges and magistrates aren't daft and the mother will have to work hard at proving that she is able to look after the children, the mantra is that the childs welfare is paramount.