I believe you can do these in any order and after all three are complete presumably the plot moves forward.  I have 2 previous playthroughs that I never went to next act.  Now I have two new playthroughs I plan to see all of the Companions (except one since 11 companions).

But really my question is what order do people do these quests in?  I usually think to save the tower until last and do the prisoner first.  The tower is in the heritage area and lots of vessals.  The ruins is in Dyrford?  The prisoner is in the mental hospital.

i usually do prisoner, tower, dyford but you can do them in any order you want. generally when i first get these quest you are prob underleveled for dyford but im sure its doable and bonus is get two companions for at least going out that way real quick.