To help safeguard our flocks, we must instruct ourselves and our children in sound doctrine, but if we are serious in doing that, we need to examine our view of the Bible itself. No charge of bibliolatry has ever been levied at a Mormon. All Mormons believe that Jesus has authority over the Bible, thus they reduce and impugn all passages that contradict their doctrine. The Pauline epistles especially suffer. Mormons clearly preach another Jesus, but unless Christians affirm the inerrancy and authority of Scripture, revelatory to the person of Jesus Christ, we have no basis for reproof.
Spiritual warfare is real.
It is especially difficult when family members are involved. I love my older sister, a devoted Mormon for 36 years, and the spiritual chasm that separates us is very painful. Let's remember our armor. The dulling of that sword must be avoided if we are to be effective. It alone testifies of the true Jesus.