Help!!!

This will be sort of long but it is something I have been incredibly worried about since the start of my husband and I trying to conceive. My mother got divorced from my biological father when I was just a baby. After that she got remarried to my stepfather when I was 4 or so. They got divorced when I was 15. It was a really bad marriage. He verbally abused my mother and older brother and sexually abused myself as a child. My mother had no idea about the sexual abuse until after they separated. He because addicted to prescription drugs after a really bad car accident and it made his manipulative, narcissistic personality worse. The thing was he was incredibly good at manipulating people into seeing him as something other than he was. Everyone who knew him thought he was a doting father and husband. They had no idea the terror he was. Anyway, during the course of their marriage they had a son together. My little brother. He was 10 when they got divorced and though he knows some of what went on we didn't feel it important to tell him what happened between myself and him. My little brother understands my hatred for him but I'm respectful and don't talk negatively about his father to him. We figure we will tell him about it when he has kids of his own in order to protect his children. 
Now that my husband and I are trying to conceive I am now incredibly worried about what will happen when we find out we are pregnancy. I don't want my step father to know but my brother still sees him every week. I don't even want him to see pictures of my child. It's why my husband and I have chosen to keep our future kids out of our Facebook profile pictures and cover photos. We have max privacy on both our profiles so we can share photos but they cannot be seen by anyone we don't approve. 
My worry is having to tell my little brother to keep any and all photos of any kids we have from his father. They will never meet him and I do not want that man to ever lay eyes on my children. It isn't a petty thing, i just don't ever want him to look at another child the way he looked at me. I never want my children to fall prey to a man like that. 
I just don't know how to tell my brother that. I want him to have a good relationship with my future kids but I don't want him to ever share anything about my kids or pregnancy with his father. How do you tell him that? What should I do? My main worry is that I'll have to tell him what happened in order to convince him not to tell his dad or show him photos.