Police say I was at fault in the accident. Am I? Can I appeal?

Usually it would be ruled that the cars behind you were following too close. In the USA most states require a lag of 3 seconds behind the car in front. Turn signal use is 300 feet before you turn if going over 35 mph, 100 feet if less than 35. We could bail out the economy if police issued tickets for not following these rules.Your problem is that you have two drivers who say you didn't signal properly. Your only hope is to stick to following too close on their part. You can't control what the driver behind you does.