If you were a passenger and not covered under the policy you may have several options, one of which is to go directly after your brother's insurance to compensate you for your bills as well as your pain & suffering. However, it is advisable to speak with a lawyer in your state so you know the full extent of your rights before proceeding.
I agree with the advice already given regarding the fact that you don't necessarily need to keep the car as long as you have a reliable estimate and plenty of pictures. First thing, of course, is to check with your own insurance company to see if you have uninsured driver coverage. If you're only planning to file a small claims suit then your uninsured coverage may be sufficient to cover your loss.
If you are planning to move out of the house it doesn't make sense that you would have to sign a new lease. It's hard to answer your question without more detail but if you are concerned about your legal rights you should speak with an attorney.
You have to be very careful before signing a release that will release ALL claims. If you do not plan to pursue any claims for property damage or bodily injury and are satisfied with the medical bills settlement then the release would be standard fair. However, if you don't feel that you've been completely reimbursed then it's important to speak with an attorney.