I CARRY THIS TEAM: When Guy Gardner is adjacent to a character with the same keyword, unless they have already been modified by this effect, modify Guy Gardner's damage value by +1 and the adjacent character's defense value by +1.

Maybe I'm not seeing it properly but if I were to run a JLI team and had multiple characters adjacent to guy, would his damage value continue to increase while the adjacent characters would only get the initial +1 defense.

Say I have 001 Batman and Ice standing next to Guy. Would he get a +2 to damage and Batman and Ice get +1 to defense or is Guy's bonus locked at +1 no matter what.

I'm confused at the they part. Does that mean the adjacent characters or Guy and everyone?

He will only get a +1 bonus. It is just checking if someone is adjacent, not how many.

The "they" part refers to Guy Gardner and adjacent characters that share a keyword with him.

When Guy Gardner is adjacent to a character with the same keyword, unless they have already been modified by this effect, modify Guy Gardner's damage value by +1 and the adjacent character's defense value by +1.

I think the section of the power I bolded is the key to this. Once Guy has had his damage value increased by +1 from being adjacent to one character, Batman say, as in your example, he has been modified by the adjacency and couldn't be further modified by being adjacent to Ice.

Correct: if "they" (Guy or an adjacent figure with the same keyword) have already had this modification then that's it: it's either "yes" or "no", not "how many".