Is money earned from working at a station that sells pork – which is forbidden and constitutes 20% of sales in a non-Islamic country – obligatory to dispose of completely or only partially, and is it permissible to give it to relatives such as parents, brothers, and a cousin's son?

It is not permissible for a Muslim to work in a place that sells forbidden things, such as your selling of pork and alcohol, because doing so constitutes aiding in sin and transgression. You are obliged to repent to Allah and dispose of 20% of the money you earned from selling forbidden items; the rest is permissible. You may spend from this forbidden money on your poor relatives, as they have a greater right to charity. Your presence in a non-Islamic country does not justify earning money through forbidden means.