the way i do it is
hands are part of an array
how you handle this array is up to you, really, but mine's defined like so
for(var i = 0; i <= 1; i++)
{
    handx[i] = 0
    handy[i] = 0
    handspd[i] = 0
    handgoalx[i] = 0
    handgoaly[i] = 0
    handrot[i] = 0
    handgoalrot[i] = 0
}
handx and handy are the position of a hand relative to the player's x and y position, rather than their position in the world
handspd pertains to how fast a hand can move in a given animation, used in a lerp function
handgoalx and handgoaly are the position the hands want to move to
handrot is the hand's rotation
handgoalrot is the rotation the hand wants to achieve
setting a hand's position is handled with a script
mine is ///hand_pos_set(hand_index,x,y,speed,rot)
hand_index refers to which hand you're setting a position for, x and y set the goal x and y, speed sets handspd, rot sets handgoalrot
if you really wanted you could add a handrotspd variable but i didn't find it necessary for my purposes here
this entire code block handles hands
//"hand"le hands hahaha
for(var i = 0; i <= 1; i++)
{
    if round(handx[i]) != handgoalx[i]
    {
        handx[i] = lerp(handx[i],handgoalx[i],handspd[i])
        handy[i] = lerp(handy[i],handgoaly[i],handspd[i])
        //handrot[i] = point_direction(handx[i],handy[i],handgoalx[i],handgoaly[i])
    }
    if round(handx[i] = handgoalx[i])
    handspd[i] = 0

    var _diff = angle_difference(handrot[i],handgoalrot[i])
    handrot[i] -= 0.25 * _diff
}
there might be better ways of handling this
but this is how i do it
from here, drawing hands is simple
i layer hand 0 behind the player, and hand 1 in front of the player
	//draw back hand and player
	draw_sprite_ext(_handindex,1,x+handx[0],y+handy[0],right,1,handrot[0],c_white,1)
    draw_sprite_ext(sprite_index,image_index,x,y,right*hsquash,vsquash,rot,c_white,1)

	//draw front hand and weapon
	draw_sprite_ext(wep_sprt[wep],0,x+handx[1],y+handy[1],right,1,handrot[1],c_white,1)
    draw_sprite_ext(sprHand,0,x+handx[1],y+handy[1],right,1,handrot[1],c_white,1)
i should note that _handindex is something that pertains to a hand's sprite index. there's only one case where a hand's sprite index changes for me so far, but it's probably smart to build a system around that too
was that good enough of an explanation