How do you get the trophy/achievement called "The Whole Gang's Here"? recruit all followers. Is that on one save or total? how do you recruit them all?

It almost has to be across multiple saves... in FO3 there were companions who would only join you if you did a certain quest or were a certain standing (good/evil). I assume F:NV is the same and to get them all you have to do it over multiple saves.

I'm having an issue with getting the chiev for getting just 1 companion... I rebuilt ED-E and had him with me for a while, then I got the dog from Freeside and did his entire questline, still no chiev. Any ideas?

maybe ed-e and rex dont count