How to convert selected HTML to Json?

What you want to do is called serializing.

//  This gives you an HTMLElement object
var element = document.getElementById('TextBoxesGroup');
//  This gives you a string representing that element and its content
var html = element.outerHTML;       
//  This gives you a JSON object that you can send with jQuery.ajax's `data`
// option, you can rename the property to whatever you want.
var data = { html: html }; 

//  This gives you a string in JSON syntax of the object above that you can 
// send with XMLHttpRequest.
var json = JSON.stringify(data);

function htmlToJson(div,obj){
 if(!obj){obj=[]}
 var tag = {}
 tag['tagName']=div.tagName
 tag['children'] = []
 for(var i = 0; i< div.children.length;i++){
    tag['children'].push(htmlToJson(div.children[i]))
 }
 for(var i = 0; i< div.attributes.length;i++){
    var attr= div.attributes[i]
    tag['@'+attr.name] = attr.value
 }
 return tag    
}

    var html = $('#TextBoxesGroup')[0].outerHTML;
    var temp = {"html":html}; 
    var obj  = JSON.parse(temp);
    console.log(obj); // shows json object  

You can use any server side language to make a json from obj.