Help identifying Greek overprints

Your stamp on the top row is a postal tax stamp, Scott # RA56.  That's an overprinted postage due stamp.

The other 5 are all overprints on a basic stamp which is either Scott # 198 or 214 depending on printing method.  If you go to the listing for that stamp series, at the end of the listing there is a note that tells you where to find overprinted stamps.  Lots of numbers starting with N, which are occupation issues in the Scott catalogues.  On the second row of your stamps, both of them have the last word of the overprint beginning with what looks like an "O" with a horizontal line across it.  That's the Greek letter theta, or a "th" sound like the beginning of "Thrace".  You have Scott #s N26 & N55 from Thrace under Greek Occupation in volume 6 of the Scott catalogues.

And for the bottom row, look at the section of occupation stamps marked "For Use in Parts of Turkey Occupied by Greece (New Greece)".  Those 1 lepton stamps come in both engraved and lithographed versions - the rightmost stamp in lighter green is certainly does not look engraved when I look at the mottled finish on the solid areas around the "1"s in the value tablets, and I think the darker greens also are lithographed as I can't see anything that looks for certain like an engraving.  Assuming they are in fact litho stamps, you have Scott #s N126 for the black overprint and N150 (used to be N145 in older editions) for the carmine overprint.  This one is red has decent value, it's valued at $12 in my 2016 edition.  Note, however, that counterfeits exist, and the different colour shade and different look on the value tablets makes you wonder.

Older versions of Scott say the normal direction for the overprint on your bottom row of stamps is to read up, but it is often found reading downward.  My 2016 edition no longer has that same footnote - the red overprints are specified as reading up but the black ones no longer say that.  They don't list any such up / down differences for the black overprints, though.  Michel does list the up / down difference and gives a slight premium to the one reading downward.

Ryan