Is it permissible to defraud someone who defrauded and took possession of money, in order to recover it after seven years have passed, and is it permissible to demand the profits of that amount throughout that period?

If your partner seizes your property and you cannot recover it except by stratagem, then there is no blame upon you for doing so. This is known as the issue of al-Zafar (gaining mastery over one's right). If the partner invests the usurped money and generates profits, you are permitted to take your share of these profits. Scholars have differed on who is entitled to these profits, and Sheikh al-Islam Ibn Taymiyyah preferred that the profit be shared between them.