Hi! You have a lot going on here! I am going to do my best to answer all your questions. Lets start with who claims you as a dependent.
One requirement to claim a dependent is that you must provide more than 50% of their support, which is the cost of basic life necessities such as food, lodging, clothing, medical and dental care, education, transportation, utilities and so forth. You also have to have earned less than 4500$ for the tax year.
Being on your parents health insurance plan does not alone qualify you as their dependent. They also have to have paid more than half of what it costs for your basic life necessities. So, it does not sound like they will be able to claim you in 2017. (provided you do live independently with your brother.) You can apply this same test to 2016 if you wish.
