Woah...lots of questions.
Will try to handle them in order.
1. Multiple Rodian Traders would still only grant a total of "Grenades 10" to any one piece. You could give Grenades 10 to a single piece 4 times, but he would still only have Grenades 10, not Grenades 40.
2. Yes, abilities that say they affect adjacent targets always hit all adjacent characters/enemies. Even if it's a Diplomat, or has Stealth, or is an ally, or something else that would keep the adjacent piece from being a legal target.
3. No, you cannot use AoOs on Diplomats if you have LOS to another enemy. The definition of Diplomat says you cannot "target OR attack" a diplomat as long as you have LOS to another enemy.
4. Lightsaber Reflect does not follow the targeting rules. It is just damage reflected back at the shooter. So, if a piece with Diplomat shoots somebody with LS Reflect, and the right saves are made/failed, then yes, the Diplomat could take the damage.
5. Energy Shield works much like you posted there. Character A attacks, Character B has energy shield. Character B rolls his save, and if he makes the save of 11, he does not take any damage. In addition, now Character A has to make a save, and if he fails that, he takes the damage instead. There are two separate saves, and if either character makes their save of 11, they don't take damage. Character A only takes damage if he fails his save AND character B makes his save first.
6. Yes, if you roll a 1 while attacking Supreme Chancellor Palpatine, you are automatically betrayed. Not sure why this was a question, as I would think this is pretty clear from the wording of Betrayal. Was the something more specific you were wondering about on this one???
In general, please go look at the official FAQ on the Wizards website. Many of your questions would have been answered in there.
