Those in my daughters life are in agreement with me. Her dad is a cop. He's seen first hand what sick idiots there are in this world. He just text me a couple hours ago, "Uh! We just interviewed a puke who penetrated his girlfriend's 4 year old daughter! If I was her dad, he wouldn't make it to trial!" I've been on the 4 yr olds side. He's talked to numerous idiots who molest young children. We make a great mix--Lily will be highly protected. (He was/is paranoid about his boys. They're not allowed to go anywhere by themselves. Up until this past year, they weren't allowed to walk home from school which is only a block away. The only people who watch his son's are his mom and dad--NOBODY else. He's even more protective/paranoid with Lily).
Yes, there are sick sick people out there who abuse children. But this behavior isn't normal, it isn't usual, and people (regardless of age or sex ) need to be able to know how to choose people to trust. Some men are sick. So are some women. But not all, and not most.
I worry for your stepsons too - they should be able to be with people besides their parents, steps and grandparents. They should have the opportunity to develop contacts and relationships with people outside their family. They will need those contacts a lot in their lives: when they apply to schools, look for jobs, move out on their own, or just when they need help in their everyday lives. I worry that isolation compounds abuse when abuse occurs.
It is, IMO, part of the work of parenting to help our children become part of a community containing people they can trust. It is part of my job as a parent to introduce my son to people who can help him with what he needs, whether that's medical attention, math homework, or just a reasonable adult he can take his troubles to. If anyone gives me a bad feeling, they don't get to be around him. If anyone hurts him, I will do serious damage. But he needs people in his life. He needs a whole support team, and I'm recruiting for him until he's old enough to recruit for himself.
I strongly recommend Protecting the Gift by Gavin de Becker as a good book on keeping children safe, which is not the same as keeping them away from people.