If your flight was uncomfortable or late it will set the mood from the start. You need to control the situation from there and invent a fun way to spend time at the airport as you wait for your flight. You can play scrabble by convincing the family that this is not going to be boring. You can also take out your digital camera and ask the family members to take photos. This will keep everyone busy for a while. If you are already on the flight then you can always play small games or watch an in-flight movie together to pass time.
A bad hotel room with a mediocre service is another unpleasant situation that you may have to deal with. The first option can be to shift to another hotel, however, if that is not an option then you can always check out the local guest houses.
Weather can be very tricky and ruthless at times, but no one has control over it and hence the best thing is to plan the vacation during the more pleasant seasons. However, if an unexpected rain ruins your vacation then you really have no option but to stay indoors and find some worthwhile activity. Getting your hands on a DVD player could make things a little better. However, if your family is not the type to stay inside, you can always get a few disposable raincoats and take everyone out for a walk in the rain.
Fights within family members are very common, and if you face such a situation on your vacation, you should take the lead and calm people down. Talk to them and make them realize that everyone is out here to enjoy and no one will gain anything from spoiling the fun.