$query= $mysqli->query("select id, name from projects limit 5");
while($project = $query->fetch_assoc()){
$news_query = $mysqli->query("select * from news where `project_id` = {$project[id]} order by `pubdate` desc limit 5");
while($news = $news_query ->fetch_assoc()){
echo $news['title'];
}
}
<img class="youtube_preview" src="preview.png" alt="" data-link="http://youtube.com....." />
$('body').on('click', '.youtbe_preview', function(e){
//меняем iframe на preview
//меняем текущий preview на iframe
});