Can someone explain the plot of DLC pls? spoilers

[Mo ~]

Spoilers alert
Hi everyone, just finished the main plot and didn't really understand it. I played the main game long ago so don't remember it clearly.
Is Mother = Sam from main game? Oooor what about seed of hope, is this some sort of 'new Sam' from main game planted? the place looks alike as from the begining of the main story.
Also what will be at the end if you dont take Mother back to Octopia? Can someone please describe in short? tyy