As mentionned, their primary of the PS is to be held on the 22 and 29 of january. I would like to clarify some points of your question and source.
FI and EM are not political parties as you would understand it from an anglo saxon perspective. They are "political movements" (mouvements politiques, I don't know if it makes a legal difference), and were founded very recently, with the presidential election as main goal. FI was founded on the 10th february of 2016, and its candidate got the support of several parties since (for the Parti de Gauche it was no surprise since it was founded by the same person). EM was founded on the 6 april 2016, and got the support of political figures (but no party, maybe as a strategic choice).
In case you are wondering why it tends to be like this. There are plenty of parties with a centrist position ( like EM) and with a far left position (like FI). PS (left), LR (right) and FN (far right) have a more dominant position in their respective political areas.
While EM may have good vote intentions in the last polls, there are bigger and older parties who also have a centrist position (also mentionned in your source, UDI and MoDem). Those may have their own candidate, and are as likely to be considered "main". Especially since the EM candidate has never held any elected office before (the election will tell us whether it played in his favor or not).
In order to take part in the election, one needs to have the approval of 500 elected officials (France has more than 36 000). You can assume that the candidates/parties who got them in the 2012 election will have them this time. In the result table of your article, overview section, all of the candidates or parties listed were already here (LR was called UMP), except EM. They are very likely to be here again. To these, one may add François Asselineau who had non negligible results in the last regional election and may get those approvals.