How to get textrange each line start and end character cooridnates using extendscript?

Not extensively tested, and not tested with sizeable text.  "ouput" is an array of the left-most and right-most characters.  You can access their position properties. 

// select 1 textFrame
var doc = app.activeDocument;
var frames = doc.selection[0];
var replica = frames.duplicate(frames, ElementPlacement.PLACEAFTER);
var item = replica.createOutline();
var objects = [];
for (var i = 0; i < item.pageItems.length; i++) {
   objects.push(item.pageItems[i]);
}
item.remove();

var temp = [];
for (var i = 0, counter = 1; i < objects.length; i += counter) {
    counter = 1;
    var row = [];
    row.push(objects[i]);
    for (var j = i + 1; j < objects.length; j++) {
        if (horizontalOverlap(objects[i], objects[j])) {
            row.push(objects[j]);
            counter++;
        }
    }
    temp.push(row);
}

function horizontalOverlap(obj1, obj2) {
   var top1 = obj1.geometricBounds[1];
   var bottom1 = obj1.geometricBounds[3];
   var top2 = obj2.geometricBounds[1];
   var bottom2 = obj2.geometricBounds[3];
   return ((top1 >= top2 && bottom1 <= top2) || 
           (top1 <= top2 && top1 >= bottom2));
}

// "ouput" is an array of the left-most and right-most chars
var output = [];
for (var i = 0; i < temp.length; i++) {
    temp[i].sort(function (a, b) {return a.left - b.left});
    output.push(temp[i][0]);
    output.push(temp[i][temp[i].length - 1]);
}

// e.g. of using "ouput", marking the positions of its elements (with red dots)
for (var i = 0; i < output.length; i++) {
    var d = 5;
    var item = doc.pathItems.ellipse(
        output[i].position[1] + 5/2, output[i].position[0] - d/2, d, d);
    var color1 = new RGBColor;
    color1.red = 255;
    color1.green = color1.blue = 0;
    item.stroked = false;
    item.fillColor = color1;
}