and other cards that say when they attack alone, for the non-unique cards, does it mean I can attack with only other Warrior's Sons to get the benefit or can I only attack with one Warrior's Sons regardless of how many I have in play?

Self-referential text always refers to the single card. So you could only trigger their ability if that one character, alone, was attacking.

The general rule is that whenever a card's title appears in its own text, it is referring to that copy and that copy only - rather than all cards with the same title.

ok, so I guess they're not as good as I originally thought, that said does their ability allow you to get past the limited location restriction then? since most gold producing locations are limited and some of the influence producing locations are also limited.

Yep. The rules for "Limited" prevent you from playing more than one "Limited" card per round. The effect on "Warrior's Sons" is a put into play effect. You are not "playing" the location they let you retrieve, so you are not subject to the restrictions on what cards can be "played."

ninja'd by the master...