T.S.
I was able to reschedule my jury duty date this summer because I was scheduled to fly my son to CA the next day. They moved it to a week after I returned.
I would call the jury commissioner and let them know that you have to go out of town to visit your dying FIL a few days after your jury duty summons. Let them know that you are concerned because if you were assigned to a trial you a)would not have the time to serve and b)you would not be able to give your full attention.
Ask to have your duty rescheduled for a later date. If you are asking to actually SERVE your jury duty, you usually have better luck than if you're asking to have your duty canceled.
Good luck.
T.