I thought they were morphs off of James and Jesse that just progressively more ugly with each subsequent generation.  First we had James, who was oaky looking, then Simon, and now Ryan--they all look like they have the same bodies to me, but just different heads.  I may be totally wrong about this--but that's my perception of them.

Up to generation 5, I think Zygote/Daz made all the native Poser people.  I think that Don was a spin off of M2--he could  use the same texture maps, except the face doesn't map quite right.  It was after Poser 5 that Poser's owners had the big falling out with Daz over the introduction of Daz Studio.  Things were never quite the same after that.  For the record I think that Don and Judy are very nice figures who never had vendor support for stuff for them.  The G2s were the only Poser native figures that there was a big push to create content for with a Platinum Club like membership available at Content Paradise at the time.