um it all looks like it works, for your problem maybe you dont have hyper triggers to make it impossible for any ally to attack another ally. Also make the "turfs" locations touching or else there will be a gap and players can change their allys.
What you could do is:
Condition: Always (well, you can change to bring)
Action: Set invincibility for Team 1(Force 1) on Location 1(Their turf/no man's land), and turn it off when they are on the other team's turf.
Be sure to preserve, and hyper triggers may help.
you may not like this idea, but oh well
Each player has 1 dark templar, and it would (unfortunately) have to be 3v3 to be fair, since I believe you need a computer player for hyper triggers. If not, you can do 4v4.
You center a whole bunch of locations on the player of different sizes, probably one large one, a medium one, and a small one. If you are on your own turf (and thus invincible) you can see people as soon as they come into your large area via forcing shared vision. If you are not on your turf, you can only become shared vision when you get in the medium range. If you get in the small range and are vulnerable, you are captured, and sent to the jail.
Using the DTs, you can really sneak up on people, though there are tell-tale signs that you are there. This can be further improved by using lots of sprite overlays and doodads.
DTs are not the only thing, of course. Anything that can move while cloaked would do this. You could even do it with zerglings, but I believe you would have to make the players cloak their zerg unit at the beginning. There would also, unfortunately, be no fighting involved, and eventually turn into a disappointing game, like all CTF games are.
Meh.. I found myself trying to read your post at least 6 times because I was watching your animation under your name... lol That's funny.
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Instead of using "Set *Player* to Ally", maybe use Invincibility? Or you could use KABOOM's idea where you have Hyper Triggers so it's impossible for them to attack an allied Player.
And if you don't know what a Hyper Trigger is, just ask, you'll have a stampede of people from Staredit.net coming to help you.