First off, any spreadsheet that will be returning JSON data needs to have been made public. This is not a hard process. The instruction can be found here.
Here is an example for returning the data from spreadsheet with the key 0Ak1itrncGIGldHNvZk9tUkhBWFJ5LXlhekxfcF9yTHc
JSON from sheet 1
Here is the code for returning the data above.
In order to do the same for your spreadsheets, just change the key so that it points to the proper workbook and the sheet reference ("od6" in the example above) to the desired sheet.