There's one player0 and nine player1, only way to differentiate between the player1's is by their x and y variables so you create hitboxes,
How complex they need to be depends on how your players move
If they move left and right and up and down completely freely all over the place you would need to create an entire box
let's assume they are both 8 pixels wide
if player0x<=player1x+8 then ; if left side of player0 is smaller than or equal to right side of player1
That's a start but it will be true even if player0 is all the way to left side of the screen and player1 all the way to the right, so we need to box it in even more..
if player0x<=player1x+8 && player0x+8>=player1x then ; and right side of player0 is greater than or equal to left side of player1
now it's true if they touch or overlap horisontally, but it will still be true even if one player is at the top of the screen and one at the bottom, so box in some more..
if player0x<=player1x+8 && player0x+8>=player1x && player1y+player1height>=player0y ; and bottom of player1 is bigger than or equal to top of player0
if player0x<=player1x+8 && player0x+8>=player1x && player1y+player1height>=player0y && player1y <= player0y+player0height ; and top of player1 less than or equal to bottom of player0
Now you have a complete box
Since boxes are square and most sprites are not you can skip the collision check if there's no hardware detection between player0 and player1
if !collision(player1,player0) then goto _skipcheck ; skips if no pixels are overlapping
if player0x<=player1x+8 && player0x+8>=player1x && player1y+player1height>=player0y && player1y <= player0y+player0height then..
if player0x<=player2x+8 && player0x+8>=player2x && player2y+player2height>=player0y && player2y <= player0y+player0height then..
that should make it pixel perfect.
This example is very good, he changes the width of player0, so the width is stored in temp5