How many of Lance Armstrong competitors were also using PEDs? ?

How many - impossible to answer.

 More than one, less than all.

I believe Jan Ullrich has admitted to using PEDS. 

Haven’t made any attempt at following up the rest. 

Not much point from this distance, trying to find villains and saints.

How would you sort out those truly innocent from those who merely didn’t get caught and didn’t admit?

Lance was busted because he refused to cooperate with WADA and even dared them to prove his guilt. He thought he was uncatchable because he'd bought off the UCI officials, but that minor detail didn't matter to WADA.

The UCI might have awarded Lance's wins to someone else, but everyone in the next 10 places all tested positive for drugs at some time in their careers; so they couldn't find anybody 'clean' to get the wins.

Lance got caught because he won too much. Plenty of others were doping too, but were never prominent enough to bother ruining.

Well humans haven't discovered how to do time travel yet. So there's no way to go back and test all the competitors when Lance Armstrong competed. Another thing to consider is what's listed as a PED today may not have been on the list back then. Bottom line is there's just no way of knowing.

Most, not all. & they need not be named. Leave them alone.