I have taken care of my niece and nephew for 2 years now. My sister has no home or no job and just expects to come and pack them up and move up north. She has never helped me support them and she stays at a hotel with her boyfriend and never comes to see the kids unless they get into a disagreement. I've spoken with Family Services in the past about this but nothing has never happened. I'm not sure if I have any rights to have the children stay with me, or..

You only have rights over someone else's kids if the court gives them to you.

File for custody with the court.

How have you been providing them with medical care? Are they of school age? If so, how were they registered in school.

Unless you have adopted them or been awarded custody by a court they are your sister's children and she can pack them up and take them whenever.

Where is the father in all this?

No you do not have any specific rights , excpet the right to file in court for guardianship