Richie,
your picture "B" also has lot of other smaller blobs scattered all over. I suspect they're most likely dirt on the negative, and I think it highly unlikely to be persons in trees. The problem I see with persons in trees is that they would only be able to climb to where the fronds branch out from the trunk, but not be able to stand on top of the tree. Such acrobatic climbing might be possible for a strong person in good condition, but that doesn't sound like a description of Fred and Amelia at the time of the flyover.
Another hypothesis is that some of the blobs are birds.
re: distance from lagoon - I was also under the impression that the seven site is more than 100 feet from the lagoon. It's a tantalizing mystery. The bones were proof that someone died there, and the evidence found since suggests the victim(s) were stranded there. If not AE and FN, who were they?