What can I do as a father as my ex has big mental health issues (please see below)?

My ex partner has mental health issues and neglects the boys, when she is down, she has said she doesn't want them, then she says she can't manage all of them, then wants them all. We have tried to organise a fair shedule but I end up having to go to her to sort the boys out every day. She is unstable and can change her mind from one minute to the next. She is seeing someone else and it's only been six weeks 

We have recently had a meeting at the school with the health visitor and a safe guarding officer and have another in January! 

I am at my parents whom have a two bed house, their lives have been turned upside down, my mum has the boys a lot as I am at work, she has had to give her job up to be on standby. If I had custody I could sort some kind of housing for the boys, arrange nusery and have help with the fees and try to maintain some stability in their lives. They are 15 months, 3 years and my step son who is 6. 

Would this be the best foot forward if not what can I do?