How can I force people to enter their email twice and not use copy/paste?

Yes, you can use a bit of JavaScript to disable the copy/paste function in their browsers. Paste this code into the Page > Settings > Custom Code > Footer section

<script>
window.onload = function() {
const myInput = document.querySelector('input[name="confirm_email"]');
if(myInput){
myInput.onpaste = function(e) {
e.preventDefault();
};
}
}
</script>

Here's a short video from our CEO explaining this, as featured in this Facebook User Community post.