Two is a "couple" and more than two or three is several. If you eat four donuts you can say you had several but you may have had too many — especially if you get a stomach-ache.
Several is a word that shows size or number when you can’t be specific or when you want to summarize. If three, four, or five of you hang out, then you're spending time with several friends. Inviting 30 people over and telling your parents that several friends stopped by would be stretching the truth and you might get grounded. For how many weeks? Possibly several.