What is the legal ruling for raising a baby girl born from zina after her mother's marriage, and is it considered an ongoing charity, knowing that the father's family might harm the child?

Your friend erred by marrying off his sister, who was pregnant from fornication, before she gave birth, thus violating the words of the Prophet, peace and blessings be upon him: "A pregnant woman must not be intercourse with until she gives birth, nor a non-pregnant woman until she has had one menstrual period." The female child born seven months after the marriage is attributed to the husband and is not disowned by him except through li'an (oath of condemnation). Adopting the child is not permissible because adoption is forbidden in Islam and no legal rulings are based upon it. However, it is permissible to sponsor her without attributing her to yourself, and you will be rewarded for that.