You and your family need much, much prayer - it would be wonderful if your brother could see a counselor, though he might not agree to go. This kind of pain in his past could certainly affect his future, especially around children. You said:
we are all tempted in one way or another. Is it fair to assume that he will be a repeat offender?Yes!! You have said that your brother refuses to have God in his life. God frees us from the bondage of sin; while we still fail as Christians, we are no longer under the power of sin. We are free; we do not, by our nature,
have to sin any longer. We can choose. Your brother is still under the power of sin! He does not have the strength of Christ nor the freedom of Salvation to help him make the right decisions. He has been shamefully abused, and if others have treated him that way, he may see no reason to not hurt someone else.
Lord, you know this man, and how he has been abused; work in his heart, and bring him to You, since no one else can heal him and make his pain into something good. His whole family has been hurt, and I pray that You would keep them in Your hands; through Your great power, and the testimony of Jesusinme, bring salvation to the ones who do not know You.