[RPG] Are there Unchained data sources for PCGen

Yes all of the above, plus the online documentation, which is marginally more up to date than the doc with the prog.

And there's some video's also. http://pcgen.org/get-help/videos/

Here's the full step by step answer

Step 1 In the PCGen data folder, create a folder labeled mystuff in the Pathfinder Homebrew folder, you structure will look like this \data\pathfinder\homebrew\mystuff

Step 2 Create a text file called "mystuff.pcc" in the step 1 folder

Step 3 Edit "mystuff.pcc" file with Notepad (or bbedit if mac) paste the following into it

CAMPAIGN:My stuff
GAMEMODE:Pathfinder
RANK:8
GENRE:Fantasy
BOOKTYPE:Homebrew
SETTING:My Homebrew Campaign
TYPE:Homebrew.PathfinderHomebrew
SOURCEDATE:2013-10

ABILITY:my_abilities.lst

Step 4 Create a text file called "my_abilities.lst" in the step 1 folder

Step 5 Edit "my_abilities.lst" file with Notepad (or bbedit if mac) paste the following into it

Pragmatic Activator
KEY:Pragmatic Activator ~ Trait
CATEGORY:Special Ability
TYPE:Trait.BasicTrait.MagicTrait
PREMULT:1,[PREABILITY:1,CATEGORY=Special Ability,Pragmatic Activator ~ Trait],[!PREABILITY:1,CATEGORY=Special Ability,TYPE.MagicTrait]
DESC:While some figure out how to use magical devices with stubborn resolve, your approach is more pragmatic. You may use your Intelligence modifier when making Use Magic Device checks instead of your Charisma modifier
BENEFIT:While some figure out how to use magical devices with stubborn resolve, your approach is more pragmatic. You may use your Intelligence modifier when making Use Magic Device checks instead of your Charisma modifier
BONUS:SKILL|Use Magic Device|max(CHA,INT)-CHA

Step 6 Load PCGen, you should see a "My Stuff" source on the left. Load that and create your character.

1. Any 2 claws. Nothing anywhere says different, just that it requires two claw hits.

2. Only once per round. The wording you quoted doesn't specify "for each two successful claw attacks...", just when it gets two. The additional claws just make it easier to proc (and do their own damage, of course). Notably, however, unlike normal rend, the wording for Unchained Eidolon's rend evolution seems to leave it open for getting one rend per round per target. I would probably rule against that in my own games, but it's certainly a valid interpretation of the wording.

3. It is not, as I answered here. Rend is applied as bonus damage to the second successful claw attack, not as a separate attack, so it doesn't gain the benefit of (or take the penalty for) per-attack effects. This includes Power Attack, flaming, or any Damage Resistance the target has, making rend a useful way to punch through DR.

4. No, again, because it's not a separate attack. That damage is already applied as part of the claw that's getting the bonus rend damage.

5. The wording on that ability seems to leave that option open as well. Even a "half-and-half" approach should work, where if you hit the target during your full attack and then hit it again before your next turn with an AoO or immediate action, the second claw should get the rend damage. That's still going to be a bit of a GM call, and will probably be ruled the same way as the "once per round per target" option from part 2, since they rely on the same interpretation of that wording.

P.S. re #5: Running through a creature's threatened area only provokes one AoO from that creature, regardless of the number of their threatened squares you run through. Just an aside, since the question implies you'd get multiple free shots in that situation.