The taxes are the big thing.
In truth, I might not start them out against the tyrant. Let their first adventure be something else...perhaps some gnolls seen in the nearby area that they are called to scout since it will take several days to get the militia together.
During this event, make the even king/baron/whatever the bad guy. When they come back, make sure the local sheriff is there to collect taxes on the coins and items they come back with ("Oh...thats a nice ring...and magical...well, looks like the taxes on that is 750 gold pieces or the ring itself..."). Suddenly they are choosing between the ring or pretty much all the money they have on them.
Also, make sure he does cause problems with the family. In truth, I'd start it off small with the local sheriff being the bad guy (at least on the outside). Have him begin to hit on one of the PC's sisters or mothers and when she spurns him several times, make sure she is found raped/killed (that might not be too PG-13 for you though). Another PC's family might have all their family holdings repossessed since some distant family member rebelled against the king and this is the punishment, etc.
Then the PC's hate the sheriff since he's the face of the lord/king. Of course, when the investigate the sheriff, they find the letters there, specifically telling him what to do (to kill the girl and other such things that, on the outside, seem like they were carried out only by the sheriff). Suddenly, things become more complicated and the adventure moves off to a new location and a new level.