Is it permissible to sell pens engraved with the sign of the cross, knowing that the father works for a company that sells them and it is the family's source of income?

We have previously clarified the prohibition of importing and selling items that bear symbols of disbelief, such as the cross. Therefore, you should advise your father to refrain from buying and selling pens that have pictures of crosses. If he insists on selling them, you will have fulfilled your duty. His insistence does not make earning from his livelihood unlawful, as he sells other permissible items. Thus, his earnings would be mixed, and eating from them is not forbidden.