I don't see why you can't do both. Since the aqua bike thing is only 56 miles, it will be a great training ride for the following weekend. Is the second event something you can choose your distance the day of? That way if you're feeling fatigued, you can choose the easier option. However I don't think that will be a problem at all to do the 100/30. Probably even the 100/60.

Is the aqua bike thing a version of the Vineman? I did the bike portion of the Barb's Race relay year before last. BEAUTIFUL country to ride a bike! I loved it.