This does sound strange but it does seem to fit. I think if it happened ANY way, we would pull apart the hinky. But I see the story as plausible.
Sometimes a bizarre outline of events is more honest then a clean-cut story.
Basically If what the step-dad is saying, the perps came in and hit him in the head, he passes out (probably on his face), they start destroying the house, find 2 of the kids and tie one up (maybe showing that they mean business, except I think that if they had really meant to harm anyone they would have hurt the girl at this point-unless the LE hasn't let the press in on that.) and then they take one of the other kids on a whim and decide to make it a ransom. The LE I remember hearing in the articles said some items were missing. A TV is big and heavy, I wouldn't rob someone for a TV. Imagine trying to load it. I would rob them for their cash, drugs, and small valuables if I was a perp.
Why I don't think the step-dad alone could have done anything,
It sounds like he doesn't have a vehicle. The 4 year old would have said something. He would have had to leave the house, and leave the children alone, I think there would be some evidence of this. I don't think he had the time to do it all alone. If the mom was in on it, then where did she drive to and from. Was she at work the entire time?
And if she wasn't involved I think she would know the step-dad's drug dealer. So if the drug dealer was involved and she wasn't involved I think she would be spilling out everything she knew to get her son back.
I just think that in family abuse usually most the family endures it, not just one of the children. I think that it makes sense to me that only one child was grabbed. Why would they want to worry and take care of more than one. And I have more thoughts but I'll stop rambling on.
But of course without all the facts, there is no way in knowing what really went on. I just hope they find this darling boy and he gets a chance to live a life. It's extremely scary to me either way this goes, if that 3 males have him or if the step-dad was involved.
If they are serious about the ransom, with the LE having this all over the news and looking for them, it's probably really hard to figure out how to collect. HOPING for that option, as it means he is still with us.