How to resize layer to a specific size and have other layers resized accordingly

Thank you.

»product1.psd« seems to feature faulty masking, though. 

A bit sloppy but you can try 

// 2025, use it at your own risk;
if (app.documents.length > 0) {
var targetWidth = 300;
var originalRulerUnits = app.preferences.rulerUnits;
app.preferences.rulerUnits = Units.PIXELS;
// the file;
var myDocument = app.activeDocument;
var theLayers = collectLayers (myDocument, []);
for (var m = 0; m < theLayers.length; m++) {
theLayers[m].visible = true;
var theLayer = smartify2010(theLayers[m]);
};
var theWidth = myDocument.activeLayer.bounds[2] - myDocument.activeLayer.bounds[0];
var theScale = targetWidth/theWidth*100;
// resize;
myDocument.resizeImage (new UnitValue (theScale, "%"), new UnitValue (theScale, "%"), undefined, ResampleMethod.BICUBICAUTOMATIC);
// reset;
app.preferences.rulerUnits = originalRulerUnits;
};
////// function collect all layers //////
function collectLayers (theParent, allLayers) {
if (!allLayers) {var allLayers = new Array} 
else {};
for (var m = theParent.layers.length - 1; m >= 0;m--) {
var theLayer = theParent.layers[m];
// apply the function to layersets;
if (theLayer.typename == "ArtLayer") {
allLayers.push(smartify2010(theLayer))
}
else {
allLayers = (collectLayers(theLayer, allLayers))
// this line includes the layer groups;
allLayers.push(theLayer);
}
};
return allLayers
};
////// function to smartify if not //////
function smartify2010 (theLayer) {
// make layers smart objects if they are not already;
app.activeDocument.activeLayer = theLayer;
// process pixel-layers and groups;
if (theLayer.kind == "LayerKind.GRADIENTFILL" || theLayer.kind == "LayerKind.LAYER3D" || theLayer.kind == "LayerKind.NORMAL" || 
theLayer.kind == "LayerKind.PATTERNFILL" || theLayer.kind == "LayerKind.SOLIDFILL" || 
theLayer.kind == "LayerKind.TEXT" || theLayer.kind == "LayerKind.VIDEO" || theLayer.typename == "LayerSet") {
var id557 = charIDToTypeID( "slct" );
var desc108 = new ActionDescriptor();
var id558 = charIDToTypeID( "null" );
var ref77 = new ActionReference();
var id559 = charIDToTypeID( "Mn  " );
var id560 = charIDToTypeID( "MnIt" );
var id561 = stringIDToTypeID( "newPlacedLayer" );
ref77.putEnumerated( id559, id560, id561 );
desc108.putReference( id558, ref77 );
executeAction( id557, desc108, DialogModes.NO )
return app.activeDocument.activeLayer
}
if (theLayer.kind == LayerKind.SMARTOBJECT || theLayer.kind == "LayerKind.VIDEO") {return theLayer};
};