A) Descendants of the slave ship. These have been living on the island
for over a hundred years. They are savage and dress in rags. They
want to take children in order to increase their (in-bred by now) gene
pool. These are the group that took the 2 children from the tail
section, and are the people that Eko and Jin saw passing when they were
hiding in the bushes.
B) Scientists / Members of the Dharma Initiative. These may have
escaped the experiments, or been abandoned on the island after the
'incident'. These people are good, but will use violence when
necessary. This group will take children to protect them from group A.
'Zeke' and the others who were on the boat belong to this group. They
have Walt safe.
I haven't heard this before (though it still may have come up)
Its not a bad idea. There could have been survivors of the Black Rock
other than Danielle. Not to mention that she has been dishonest about
a few things.
I don't think the black rock was a science ship AND a slave
transport.
I don't think She was on the island 16 years (but she didn't exactly
lie about that either)
She obviously had something to do with the abduction of Claire.
And I don't think she killed EVERYONE from her crew. I am leaning to
the idea that maybe Ethan and Goodwin could have been on the Black
Rock with Danielle.