Satsuki's absolute favorite hobby is napping. This is fairly unknown, as she prefers to hide when napping. In the public eye, she is known for training with Kenjutsu or Taijutsu during her free time where she isn't missing or at the office. Despite not being pleasurable or a hobby, she spends most of her time performing kage duties, mostly paperwork. She enjoys assigning and debriefing missions and she has grown fond of individual training sessions, wherein she learns about new people. This is much more preferable to her than reading some file.
Isao has no hobbies. His life is entirely revolved around work. For this reason, he is widely known to be doing something at all times, whether out on a mission, reporting about a mission, training in the field with advanced Kenjutsu or basic Taijutsu, or out in the library reading up on techniques, particularly Fuuinjutsu. He does practice Fuuinjutsu in libraries on occasion, but typically prefers the privacy of his own home. Ninjutsu is generally trained in open spaces far from the public, so it is assumed that whenever one can't find him, it's because he's using powerful techniques likely to kill you. He does visit restaurants for the majority of his meals, but almost always in solitude. Those who know him assume that he is secretly some kind of connoisseur, but in truth, that is when he practices his Genjutsu. His greatest secret is that the first sentence of this paragraph is entirely false. Truthfully, he is not as devout at Ninjutsu practice as most people think; he is usually off in hiding practicing one of a variety of hobbies that he would be abhorred for anyone to find out about. These include: