Some more info needed to answer your question.
1. Are the stations that you have downloaded and inserted into your layout passenger active - I know you said they have passengers but what is their active setting? - most (all) passenger active stations are usually set to supply an initial number of passengers and then so many per hour - but it is always worthwhile checking the settings.
2. Is your passenger rolling stock also passenger active - from your description I get the impression that this may be the case but it is again worthwhile checking.
3. (and this is possibly the cause of your problem) when you issue a "Drive To" command do you follow it immediately with a "Load" or "Unload" (with passengers it does not make any difference) command? Insert both into the trains order list at the same time - do not wait until the "Drive To" has been executed before inserting the "Load/Unload".
Peter Ware