This Multifield.js is working with all the widgets like drop-down and checkbox functionality.

Multifield.js

(function ($, $document) {
    var DATA_EAEM_NESTED = "data-eaem-nested";
    var CFFW = ".coral-Form-fieldwrapper";
    function isSelectOne($field){
             return !_.isEmpty($field) && ($field.prop("type") === "select-one");
         }
         function setSelectOne($field, value){
             var select = $field.closest(".coral-Select").data("select");
             if(select){
                 select.setValue(value);
             }
        }
         function isCheckbox($field){
             return !_.isEmpty($field) && ($field.prop("type") === "checkbox");
         }
         function setCheckBox($field, value){
             $field.prop( "checked", $field.attr("value") == value);
         }
         function setWidgetValue($field, value){
             if(_.isEmpty($field)){
                 return;
             }
             if(isSelectOne($field)){
                 setSelectOne($field, value);
             }else if(isCheckbox($field)){
                 setCheckBox($field, value);
             }else{
                 $field.val(value);
             }
         }

    //reads multifield data from server, creates the nested composite multifields and fills them
    function addDataInFields() {
        $(document).on("dialog-ready", dlgReadyHandler);
            function dlgReadyHandler() {
            var $fieldSets = $("[" + DATA_EAEM_NESTED + "][class='coral-Form-fieldset']");
            if(_.isEmpty($fieldSets)){
                return;
            }
            var mNames = [];
            $fieldSets.each(function (i, fieldSet) {
                mNames.push($(fieldSet).data("name"));
            });
            mNames = _.uniq(mNames);
            var actionUrl = $fieldSets.closest("form.foundation-form").attr("action") + ".json";
            $.ajax(actionUrl).done(postProcess);
            function postProcess(data){
                _.each(mNames, function(mName){
                    buildMultiField(data, mName);
                });
            }
            //creates & fills the nested multifield with data
            function fillNestedFields($multifield, valueArr){
                _.each(valueArr, function(record, index){
                    $multifield.find(".js-coral-Multifield-add").click();

                    //a setTimeout may be needed
                    _.each(record, function(value, key){
                        setWidgetValue($($multifield.find("[name='./" + key + "']")[index]), value);
                    })
                })
            }

            function buildMultiField(data, mName){
                if(_.isEmpty(mName)){
                    return;
                }
                $fieldSets = $("[data-name='" + mName + "']");
                     //strip ./
                mName = mName.substring(2);
                var mValues = data[mName], $field, name;
                if(_.isString(mValues)){
                    mValues = [ JSON.parse(mValues) ];
                }
                _.each(mValues, function (record, i) {
                    if (!record) {
                        return;
                    }
                    if(_.isString(record)){
                        record = JSON.parse(record);
                    }
                    _.each(record, function(rValue, rKey){
                        $field = $($fieldSets[i]).find("[name='./" + rKey + "']");

                        if(_.isArray(rValue) && !_.isEmpty(rValue)){
                            fillNestedFields( $($fieldSets[i]).find("[data-init='multifield']"), rValue);
                        }else{
                                var select = $field.closest(".coral-Select").data("select");
                                if(select){
                                    select.setValue(rValue);
                                }
                                else{
                            setWidgetValue($field, rValue);
                            }
                        }
                    });
                });
            }
        }
    }
    function fillValue($field, record){
        var name = $field.attr("name"), value;

        if (!name) {
            return;
        }
        //strip ./
        if (name.indexOf("./") == 0) {
            name = name.substring(2);
        }
        value = $field.val();
                 if( isCheckbox($field) ){
                     value = $field.prop("checked") ? $field.val() : "";
                 }
                record[name] = value;

        //remove the field, so that individual values are not POSTed
        $field.remove();
    }

    //for getting the nested multifield data as js objects
    function getRecordFromMultiField($multifield){
        var $fieldSets = $multifield.find("[class='coral-Form-fieldset']");

        var records = [], record, $fields, name;

        $fieldSets.each(function (i, fieldSet) {
            $fields = $(fieldSet).find("[name]");

            record = {};

            $fields.each(function (j, field) {
                fillValue($(field), record);
            });

            if(!$.isEmptyObject(record)){
                records.push(record)
            }
        });

        return records;
    }

    //collect data from widgets in multifield and POST them to CRX as JSON
    function collectDataFromFields(){
        $(document).on("click", ".cq-dialog-submit", function () {
            var $form = $(this).closest("form.foundation-form");
            var $fieldSets = $("[" + DATA_EAEM_NESTED + "][class='coral-Form-fieldset']");
            var record, $fields, $field, name, $nestedMultiField;

            $fieldSets.each(function (i, fieldSet) {
                $fields = $(fieldSet).children().children(CFFW);

                record = {};

                $fields.each(function (j, field) {
                    $field = $(field);

                    //may be a nested multifield
                    $nestedMultiField = $field.find("[data-init='multifield']");

                    if($nestedMultiField.length == 0){
                        fillValue($field.find("[name]"), record);
                    }else{
                        name = $nestedMultiField.find("[class='coral-Form-fieldset']").data("name");

                        if(!name){
                            return;
                        }
                        //strip ./
                        name = name.substring(2);
                        record[name] = getRecordFromMultiField($nestedMultiField);
                    }
                });

                if ($.isEmptyObject(record)) {
                    return;
                }
                //add the record JSON in a hidden field as string
                $('<input />').attr('type', 'hidden')
                    .attr('name', $(fieldSet).data("name"))
                    .attr('value', JSON.stringify(record))
                    .appendTo($form);
            });
        });
    }

    $document.ready(function () {
        addDataInFields();
        collectDataFromFields();
    });

    //extend otb multifield for adjusting event propagation when there are nested multifields
    //for working around the nested multifield add and reorder
    CUI.CustomMultifield = new Class({
        toString: "Multifield",
        extend: CUI.Multifield,

        construct: function (options) {
            this.script = this.$element.find(".js-coral-Multifield-input-template:last");
        },

        _addListeners: function () {
            this.superClass._addListeners.call(this);

            //otb coral event handler is added on selector .js-coral-Multifield-add
            //any nested multifield add click events are propagated to the parent multifield
            //to prevent adding a new composite field in both nested multifield and parent multifield
            //when user clicks on add of nested multifield, stop the event propagation to parent multifield
            this.$element.on("click", ".js-coral-Multifield-add", function (e) {
                e.stopPropagation();
            });

            this.$element.on("drop", function (e) {
                e.stopPropagation();
            });
        }
    });

    CUI.Widget.registry.register("multifield", CUI.CustomMultifield);
}(jQuery, jQuery(document)));

Line 53 function fillNestedFields .Once addbutton is clicked All multifield items aren't ready. Use the CoralUI ready event handler in this case to prepopulate the multiflied items.Below is the sample code

                $multifield.find(".js-coral-Multifield-add").click();
	            Coral.commons.ready($multifield, function(){
                		_.each(record, function (rValue, rKey) {
		                    $field = $multifield.find("[name='./" + rKey + "']").get(0);

		                    $($field).val(rValue);
		                });