Very different mission designs...
The idea of Fractional ownership is based upon having multiple aircraft with multiple owners so that mathematically, most owners will have access to "their" aircraft when they need to fly. From what it looks like, you will have one aircraft with multiple owners... a bit more difficult to satisfy all the partner's individual needs.
You say that you will be "flying a lot in California" and occasionally going to Hawaii so you must have already collected identified some mission data. (If you're going to Hawaii, forget about reliable 800 trips in the winter when everyone wants to go. Starting a trip without a wet footprint may be challenging). What is your average estimated stage length? What will be your estimated average pax load? Do you need baggage space for skis? Golf clubs?
You say that:
"Both planes can fly long distances. Is there one that is better than the other, or is it just a matter of personal preference? Which one is more comfortable for longer haul flights? Another aspect I was considering is the safety factor of having 3 engines on the Falcon. I am pretty new to this, so every advice will be greatly appreciated!"
I'm not sure I'd clasify the 800XP as a long distance aircraft at around 2,500 nm/LRC but the Falcon 50EX advertises about 3,100 nm/.80. Not bad.
The question about personal preference is subjective.
Yes 3 engines are better than two unless you're thinking about operating cost, maintenance, etc...
Both are great airplanes for what they were individually designed to do. You may need to do a bit more research before deciding on any aircraft. There are others that may better fit your mission profile.
Good luck,