All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If you cannot influence your family members by what you say to them, then try to convince them to visit the nearest Islamic center. If they accept, then explain their case to the people working in the center and tell them to be soft and act wisely with your family members as Allah Says (what means): {Invite to the way of your Lord with wisdom and good instruction, and argue with them in a way that is best.} [Quran 16:125]
If you fail to convince them to go to an Islamic Centre, you may organize a meeting between them and a good Da'iyyah (a person who calls to Islam) so, that he calls them to Islam. You may also get some cassettes, pamphlets or other good Islamic aids to help them return to the right religion. But more importantly keep on supplicating for them that Allah guides them to the right path. Do not get bored or pessimistic. Keep on trying by all available legal means. Choose good timing and appropriate speech and do not hasten; keep on following a step by step progression. Know also that what they need first is to recognize Allah, their Lord as He is their Creator, their Sustainer and their God. This can be achieved only by explaining to them the meaning of “Laa Ilaaha Illa Allah Muhammad Rasoolu Allah” (None has the right to be worshipped but Allah and Muhammad is His Messenger).
They should love Islam, believe in it, accept it and abide by its rulings. They should also be proud of Islam as it is the only true religion. Abiding by the rulings of Islam means performing its obligations (Prayers, Zakaah, Hajj and Fasting) and avoiding its prohibitions (Zina –fornication or adultery, alcohol, etc.).
Allah knows best.