Centeral Locking not working on Astra 54 plate ?

Centeral locking not working have tried re synic but not working at the moment can only open the driver side door and back passanger door, but sometime even they wont open and have to use the key. It all started with just the driver back passanger door not working.
Please help any ideas welcome I don't feel safe driving the kids around in car when the doors wont open but cant afford to take it to the dealership.