I don't think you are in over your head if you do not try to learn all twelve at the same time!! Just give yourself lots of time to learn them, and don't expect fluency in any language right away. I am learning Mandarin Chinese right now. From people I talk to, it can take ten years for somebody native in English to become completely fluent in Chinese! This number is not set in stone though. Some people take much less time than that, some never become fluent. It all depends on the person and how much time they are willing to put in it. Also, it would probably take a lot less time to become fluent in a language more similar to English. Its a good time to start now since you are young. Here is what I would do.
1. Pick the language you want to learn most. I would suggest picking a language that is common in your area if possible. For example, if there are a lot of Spanish speakers in your area, learning Spanish will be easier because you can practice it more.
2. Research that language and see what languages are closely related to it. For example, of the Languages you picked, French is probably the closest to Spanish. So, if Spanish was your first choice, you might want to do French next.
3. Immerse yourself in the first language you chose. A computer program wont be enough by itself because you will have to engage in actual conversation as much as possible. Do anything you can to expose yourself to that language. If possible, take a class, rent movies in that language, listen to music in that language, and most importantly talk with other people in that language as much as you can. Get feedback from those you talk to.
4. When you feel yourself becoming more comfortable in the first language you chose, move to the next language. Only do this if you can still continue to practice the first language daily. Once you stop using a language, you will forget it. If you feel overwhelmed with learning two languages at once, go back to just learning one. I wouldn't focus on more than two languages at a time.
5. Do not expect miracles. It takes years to learn just one language, so don't get discouraged.
Learning a new language is so rewarding. You will meet many people, learn about a new culture, and open up future opprotunities you may have never imagined. Best wishes