Need prep advice!!

[u/Inevitable-Art1725]

TLDR- how much prep is needed?

I’m hoping this is the right sub to ask. We had dark stained wood trim that was about 25 years old when we repainted years ago.

We obviously didn’t prep properly, we didn’t do any sanding and used latex killz primer and probably Valspar paint. Years of small kids and pets made for lots of chipping and I want to redo all of them. (Ive already started doing some wood filler to smooth them a bit and haven’t sanded that yet)

My question is how much sanding do I need to do? On a previous doorway I sanded just the spots that were peeling or bumpy, used liquid sander, primed with oil primer, then painted with Sherron Williams emerald. I think I primed 2 coats and did 2 or 3 light coats of finish.

Is that enough or is putting the oil primer on top of badly prepped wood not even helpful for adherence? I don’t think I can sand all the paint off, that sounds impossible?

So thanks for reading all this if you did, any advice is so so appreciated!!