Not taken the wheels off yet,but are the sensors attached to what i see is a wire running to near the brake caliphers??One of the most common causes of ABS and ESP faults is down to faulty ABS sensors so it may be worth having then checked out.
Have you actually tested the brakes in a safe area to ensure the wheels don't lock under heavy braking?
Is there a plug in diagnostic tool you can buy on ebay??You really need to run diagnostic to see which wheel sensor is faulty. fingers crossed it will be a wheel sensor otherwise you are looking at a new abs pump which will cost over a grand.