Yeah I saw this, and it was a previous episode of PBS-ST that gave me the ideas I was talking about previously. Here they just go into more detail. It's nice they give a fuller explanation for Hawking radiation, rather than the simplified particle-antiparticle formation on the event horizon.

I would imagine they don't collide because quantum mechanics forbids it. Something about them having to both share the same quantum state in order to actually collide. I'm guessing here but you'd have to imagine these things are moving at near light speed. Either quantum mechanics forbids it, or it's so ludicrously unlikely that they will collide that they basically don't.

I've always wondered this with regular stellar black holes, when they collide. Here we have two singularities presumably merging into one. I've always thought it was more likely they would orbit each other at a Plank distance or something like that, rather than actually merge. I never could get comfortable with something that occupies the smallest space it's possible to occupy, colliding with something else of equal size. There's quantum effects here that are well beyond my grasp. I'm not sure an actual collision ever takes place, though it would seem like it to an observer who can't make perfect measurements.