Your mother's and brother's green cards are in no way affected by your staying or leaving. You and your brothers received yours based on your mother's marriage but now that you have them all belong to the individuals. Stop worrying about that possibility.
You need to understand that there are residency requirements to you maintaining your green card and be able to plan these into your schedule.
It was unfair for your parents not to discuss the plan with you before you were surprised by it. You sound very mature for your age worrying about your mother and siblings being adversely affected by your decisions. Both of yuor parents should be very proud of you.
Your concern about your school in Paris is a valid concern. I hope your father can meet with the administrators so they can hold your spot. Many young people want to have the opportunity to attend school in the US but prefer to have a really good knowledge of English before doing so.
You should suggest to your mother that she consult an immigration attorney since she may not be fully aware of the requirements. If she does, she may be willing to take you with her as well so that you are not getting information second hand. You mother needs to understand that even if you lose your green card now, based on her marriage, it is relatively easy to get another as long as you meet the age requirements. She needs to get this information from the immigration attorney so she sees that there are many options for you. Right now your school should be a very important consideration.

