My family do not pay khums but I pay khums on the money I get (none of us have jobs so we get welfare from the state and we live in Sweden). We pay for food together so the money get mixed, is this food that I eat haram? If it is haram what should I do so I eat only halal food?

Estimate what you have eaten and pay its Khums, or request from your Marja Taqlid to ignore the past provided that you will pay for the future.