The Awake of June 2010 in an article about "Keeping Stress Under Control" had this sage advice....
"God expects us humbly to acknowledge that we have physical, mental, and emotional limits and that we cannot do everything we would like to do. As difficult as this can be, we may need to learn when and how to say no to demands that exceed what we realistically can handle."
A scripture which I shared with the worried father of an elder who was being over worked by the WTBTS / IBSA and had a nasty coronary is...
Micah 6:8 - "He has told you, O man, what is good. And what is Jehovah requiring of you? Only to exercise justice, to cherish loyalty, And to walk in modesty with your God!"
So the WTBTS's demands on your dad and many Bro's may be seen as quite unreasonbable when compared with that Awake and scripture!.