The Ruthlessness ability reads that "after you perform an attack that hits, you must choose 1 other ship at range 1 of the defender (other than yourself). That ship suffers 1 damage." My question is if only a ship from your squadron is within range 1 of the defender than does it have to hit that or does the "other than yourself" include your whole squadron or just the ship equipped with that ability?

No, it does not include the rest of your squadron. If the only other ship within range 1 of the target is another of your ships, it's about to cop some friendly fire.

What does the card say

It says you have to perform an attack that hits

It says you have to select another ship within range 1of the defender that isn't the attacker

it says that ship suffers 1 damage

simple

The flavour text that comes with the Decimator should make it plain what is happening.

What does the card say

It says you have to perform an attack that hits

It says you have to select another ship within range 1of the defender that isn't the attacker

it says that ship suffers 1 damage

simple

This feels a little unnecessary.

If the card said "that isn't the attacker", I doubt the question would have been asked. But it doesn't - it says "other than yourself".

So the real question here (as the OP actually articulated) is "What does 'yourself' mean?" Which is a question that gets asked on a near-daily basis. "You" in X-wing refers to the ship with the ability, not to the player. So "Yourself" means the attacker. Any other ship is fair game.

I don't think condescension is the right response to a player's first post, but if you're going to, you should at least make a point of understanding the actual question.