I don't think you'll have a problem with seasickness, but I just wanted to say that when we went, no-one on our boat had any sickness or upset tummies. The boat had some sort of a filter system and used the filtered water for washing salads and cooking. Remember to take 2 water bottles each, one for drinking from, and another for using to clean your teeth. Also take hand/wet wipes or a small bottle of alcohol rub for cleaning your hands, some of the money is really grubby, so its a good idea to be careful when out. We have eaten in 'local' restaurants and had no problems. Mind you, I have seen the Felluca guys just dip a glass into the Nile and drink the Nile water! Wouldn't fancy that, but they seem to be ok.
Hope you enjoy yourselves, I'm hoping to go back again next year.