@mbmorandi,
The problem here is in the HTML, not the JavaScript. Each of your questions and answers has an id tag like id="Q1" or id="A1". If you just copy and paste the code from the first 3 questions, your fourth question will reference the id you pasted and will open that question. So for each of your additional questions after Q3, make sure you change the ids to match - Question 4's id should be id="Q4" and the onclick="expand A4" while the Answer 4's id should be id="A4". You have to change these by hand for each new question you add to the FAQ.