When I have sent all 3 people to the fountain it will not recognize they are there it just tells me to go find them still so it wont let me continue with the second part of the quest.
I have tried different saves on various difficulties and even in hardcoe.
I have deleted and reinstalled the dlc.
I have recruited each in turn as companions.
Nothing will work and I have now given up.

This is talked about all over the internet as being a X360 glitch and i feel a little disgusted that such a large company would release something that they know has such a massive glitch still. I feel I have been duped into paying ￡7.99 for something that was never going to work, and that's forgetting about the equally big GOD/DOG glitch where if you take him as a companion you can't get rid of him and even if you kill him he still stays as your companion.

If anybody can offer any help with this issue now it has affected the PS3 as well i would be forever in your debt

Yup...having the exact same issue!!!...wtf is going on!!!!? what's even worse is that I accidently saved over the wrong file so it looks like I'm going to have to start the whole game over from the beginning. My order was Dean-Veronica-Dog with Dean as my companion, I tell him to part ways and he returns to his hideout in the residential area.

$10 down the drain.

This issue typically only occurs when you have a game save that did not have the game update/patch installed.

Best thing I can recommend is rolling back to save before you started Dead Money and make sure the game update is installed. If it's not installed (or is deleted) at any point while you're playing the Dead Money content, this issue can occur.