No genuine science expedition would willingly take along a woman who was seven months pregnant.
Danielle was not seven months pregnant when the expedition left. According to the timeline, Alex was born in April 1988, and they sailed from Tahiti the previous November, when Danielle would have been only a couple months pregnant. They would have departed from France even earlier than that, probably October. It is possible/likely she did know she was pregnant until the exhibition was underway.
The French expedition has nothing to do with Widmore or the DHARMA Initiative but is a third-party attempt to discover the Island. The fact that the team is armed with rifles indicates they were doing more than charting ocean currents. France has several colonies and territories in the South Pacific, and it's possible someone in one of them heard the Numbers just as Leonard Simms and Sam Toomey once did. This information eventually came to the attention of someone who knew about DHARMA and the Island, who then dispatched the expedition to try and locate the Island. At least one of the crew members is aware of the real mission, even if the others are in the dark.
Maybe the third party that could've sent the team was Eloise. She would've been exiled/gone from the Island at this point, seeing as Widmore was now the leader in 1988.
The science expedition are 'innocent' in the sense that none of them had prior knowledge of the Hanso Foundation, DHARMA, Widmore or The Others. Like Leonard and Sam, they somehow heard the transmission. It was likely they were brought to the Island through the influence of Jacob, as the members of the expedition were candidates.
Danielle was seven months pregnant when she landed, therefore when the events leading to her team's demise occurred two months later. She would close to giving birth. The Others caused these events to capture Alex.
Ben's instructions from Widmore were to kill Danielle. They did not know there was a baby until Ben returned with her, which angered Widmore, who thought he should have killed her too.
The entire story was a totally phony one made up by Danielle Rousseau and known by Ben to be false. Multiple lines of evidence show that the Island was elsewhere (in or near Fernando Poo, Equatorial Guinea, half a world away) and so could not have been reached by such a vessel from Tahiti, and that the time jumps were phony as well; Jin knew that both his airline crash and time jumps were phony. So events could not have occurred when and where they were claimed to have. Numbers transmissions in voice on radio are commonplace, and would not have been the object of a science expedition, and it is unlikely someone at that stage of pregnancy would have been taken on an expedition of any kind in such a craft. The others alleged to have arrived via B612 were conveniently said to have died. Alex was born elsewhere and may or may not be related to either Danielle or Ben, although she may have been convinced by Ben that she was Rousseau's daughter whether that was true or not. Danielle's supposed assassination by gunfire can be seen to be phony by the fact that the water bottle that was supposedly shot developed one hole, not two, and Lost was very careful to have (and call attention to) entry and exit wounds or holes from gun shots; however, Alex was convinced the shooting was real, getting her supposed mother conveniently out of the way if that's who Alex thought she was.
The entire story would have been the part of the Big Store grift (a long con with many accomplices and elaborate locations) on Said, Sawyer, Desmond, Juliet, C.S. Lewis, and a few others who were not in the know, convincing them that Ben, Rousseau, and Charles Widmore had been at that location much earlier than had actually been the case. Ben's story of having been told by Widmore to kill the Rousseaus was to establish himself as the good guy and Widmore the bad guy.
Symbolic relationship to overall plot
Lost, especially in season 6, was much taken up with miniature versions of the main plot, as clues to the audience for its solution. The story of Alex Rousseau, who was falsely claimed to have been falsely claimed to have been (note double deception) Ben's daughter mirrors the main plot, in which Kate's daughter was pretended to have been adopted by Kate from Claire, when actually Claire's pregnancy and delivery by Kate had been faked with the cooperation on the spot of Jin, to fool Sawyer -- all in service of a Lost Heir grift to usurp Hanso's holdings.
The name Bésixdouze appears to be a reference to Antoine de Saint-Exupéry's Le Petit Prince and, thus, the name of the episode. In the novel, the Little Prince comes from a planet/asteroid known as "B612", or in French, bé six-cent-douze.