Rookie scale construction questions

[Mastema]

I've been playing bass for a while now, and figured I should finally try to figure out this theory thing.

So I have the major scale formula down (W-W-h-W-W-W-h). From what I understand, to make a minor scale from the major scale of the same key, you use root-2-b3-4-5-b6-b7-octave.

I thought it would be a good exercise at work while waiting on stuff to compile to put down all 12 keys and write out each major and minor scale and then pick out the relative minor.

A couple questions:
Db minor: Db-Eb-Fb-Gb-Ab-Bbb-C-Db
The double flat is throwing me off. I looked into it on the good ol' interweb and all I could find out was this was rarely (if ever) used. Is this accurate? Can someone explain why?

Eb. This one's been giving me a headache.
For Eb major, I have: Eb-F-G-Ab-Bb-C-D-eb
For Eb minor, I have: Eb-F-Gb-Ab-Bb-Cb-Db-eb

Now, when I checked my work my Eb major was correct but the Eb minor was listed as having a natural D rather than the D-flat. But that breaks the flatted 7th "formula" I've been using to make my minor scales.

I'm not 100% up on my standard notation, but one of the same websites that listed the scale as having a natural D had the scale out in standard notation. The note was on the D line, but it had a b over in the key signature area which I think means it's flatted. But why is this inconsistant with the other notes in the scale and why is it listed everywhere else as a natural D?

I'm assuming it's just some silly mistake I'm making, but if it's some exception or theory "gotcha" could someone please spell it out for me. I'd really like to understand this stuff. Thanks!