how to drain brake fluid and start over?

The easiest method to "replace" as much brake fluid as possible takes 2 people and a few wrenches. Take a turkey baster and suck all the fluid out of the brake master, there should be 2 seperate section in the brake master. Empty them both out. Then fill them both up with DOT 3 brake fluid. This will replace most of the fluid. To complete this process requires the help of someone to pump the brake pedal. Next you will need to locate the brake bleeder valve for each wheel. The process is basically this. step 1: put a wrench on the brake bleeder valve loosen then snug back up step 2: have you helper pump the brake pedal 3 times and then hold the pedal pushed. You will then open the bleeder valve and brake fluid will squirt out, have helper keep holding pedal, it will go to the floor. Have them say floor when the pedal reaches the floor. step 3: you now close the bleeder screw and repeat all 3 steps 2-3 times for each wheel. During this process you will have to refill the master with fluid. Good luck. Honestly I typically recommend taking a vehicle to a Certified repair station for this kind of stuff. Brakes are nothing to "Try" to fix on your own...

You screwed up big time. Oil is not compatible with brake fluid. Brake fluid is a glycol, not an oil. Oil destroys the rubber parts in the brake system. Your car is now junk. You would need to REPLACE all the calipers, the reservoir and master cylinder, the ABS pump, and completely flush all the lines out with alcohol and compressed air, and install a completely new brake system, as your existing one is ruined, and it's surprising you haven't had a major accident yet.