Wa alaikum salaam brother,
It seems that right now you are feeling confused about what to do about your marital situation. Alhamdulilah, you married a good woman who is good to you, however, you have just found out that she was concealing information from you which has cast doubts in your mind now.
Whilst I can’t answer your question regarding the Islamic rulings on your right to divorce her and what Islam says about raising orphan children as these are questions for the scholars, I can support you with information on the psychological side of things.
If you choose to continue in the marriage, it is important that you leave behind any hard feelings that you have toward her as a result of what she hid from you and be prepared to face the challenges that may arise. If you are unable to do this then you may continue to face difficulties. It might be best to begin by confronting her about it and how you feel betrayed that she kept it from you until after you were married which was not fair. Certainly, Islam places marriage amongst one of the most respected institutions and does much to protect it and ensure peace and respect between spouses. She needs to understand that what she did was deceptive and how this makes you feel. How would she feel if it was the other way around; that you had 6 children but chose not to reveal this t her until after you married. She would quite likely feel as devastated as you are.
If this is the route you chose to take, then understand that it is best that you find it in your heart to forgive her shortcomings, otherwise, it will continue to be an ongoing issue for your marriage. Forgiving people can be difficult when they have wronged you, but always remember that we can draw on the character of the Prophet Muhammad (SAW) in remembering how he forgave people who had wronged him to the most extreme of levels. Remember also, that we all do wrong in one way or another and we pray for the Mercy of Allah, and if we can expect Allah to forgive us, then we have to be prepared to forgive others too. This forgiveness will help to bring a softness in your heart that will allow you to move through this situation with less difficulties in your marriage.
If you find yourself unable to accept what has happened and chose to pursue a divorce instead, then ensure that you get support from your loved ones to support you through what will be a difficult time. Divorce is not an option you can go back on, so make sure you are absolutely sure about it if you chose to do so and move forward with confidence that you did the best thing for you.
It is a difficult choice to make. On the one hand, you are already married and you say she is a good woman, but at the same time, she deceived you and she has even more children than she told you which you are finding to be a bit of a burden. At this time, you can make istikhara and ask Allah to guide you to make the best decision that will be good for you and your wife as well as being most pleasing to Him. Continue to find solace with Allah that you will feel happy and content with whatever choice you make in the confidence that you doing it to please Him.
May Allah guide you to make the best choice that you will be content with and will please Him. If you continue in the marriage may He bring ease in your affairs and if you pursue divorce may He make it smooth and easy for you. Either way, may He comfort you in His remembrance.
Disclaimer: The conceptualization and recommendations stated in this response are very general and purely based on the limited information provided in the question. In no event shall AboutIslam, its counselors or employees be held liable for any damages that may arise from your decision in the use of our services.