My mother has family who hate her and only want money from her, this is not a assumption but rather something that is a fact.

Does my mum still have to keep relationships with them like calling once a year and doing her part in not severing ties of kinship or can my mum cut them off?

We can’t give them anymore money because they were stealing from us.

Since they are family it is haraam to cut off with them. If they are being disrespectful they will deal with the consequences of their actions. On the day of judgement God will ask you what you did. Helping out family is also a way to receive mercy. If you are able to help out, do it for God not for them. If you can’t help out then that is another issue.