Help with a Poisoning Script

[Zacyiia]

I am writing a plugin that will reduce the party's hp by 10 points per step If they should enter a map without the right key Item.
What I plan on having this plugin check for is the following:

-If one of eight map events are present

-If one of these map events is present; check for one of the nessacery Key Items
Ex: Fire Power Glove / Wind & Fire Power Glove / Fire & Water Power Glove

If the player enters an area where a Fire Event is present and has a Power Glove upgraded with Fire, then no health will be lost.
If the player enters an area where a Fire Event is present and has a Power Glove, but is not upgraded with Fire, then they will lose 10 hp each step.

Right now my plugin is able to check for the Game Variable 1 (which I named fire), and if the variable is not equal to 1, then the
player takes -10 hp each step. I am not really sure how to make the two checks above so that I can just use the Key Item instead of variables. Also I don't know how to affect the entire party at once in regards to $gameActors.actor().gainHp().

Here is my code so far:

(function() {
Game_Player.prototype.executeMove = function(direction) {
this.moveStraight(direction);

if ($gameVariables.value(1) != 1 ){
$gameActors.actor(1).gainHp(-10)
$gameActors.actor(2).gainHp(-10)
$gameActors.actor(3).gainHp(-10)
}
};
})();