Whether to share bypass capacitors
No, you should have one cap for each. Well, it may in fact work even with no capacitor, but if you want to be sure, just do what you have to do. The capacitor reducec radiated emissions, ensures stable voltage and provides switching current. It's very important. Of course, pay attention to layout- connect the capacitor to the ic with shortest possible trace, use planes, etc. 

Having said that, i bet it will work good enough with one cap. But do prepare pads for the other one.