The pre emergent you put down is for grassy weeds like crabgrass. The weeds you took pics of are broadleaf weeds, which a pre emergent has no control of.The pre-emergent didn't get it so it may be something I'll need to treat immediately.
I don't know exactly what weeds those are in pics, purslane, spurge?... but it really doesn't matter. What I will say is that if you want to get ride of them you need to use a broadleaf herbicide. Something in the Trimec, 3-way herbicide family...mmmm 3-way.