Just as an added measure, you may want to call DL to link your two PNRs. No, it does not become one, but DL will include a note in each PNR to improve the likelihood that you will travel together. Absent this, there is no relationship between the party of 3 and the party of 1.

Also, keep in mind that this is a codeshare with AF on AF metal. DL has a portion of the inventory, so if it shows 0s, then DL won't sell additional tickets in that fare class. In the mean time AF may still have inventory to sell. My bet is that you will fly together, but you may not sit together (not always a bad thing).

Last thing . . . Get onto the AF site with the DL confirmation number (yes, it now works) and see if there are seats to choose; if so, then you can select a seat that way. I've had success with this route recently.