Welcome. Did they go out at the same time?
Forgive me for asking this, but you have checked the balance control?
OK, For some reason I though it was the drivers front and rear. Sorry. Do you have a multimeter to test the resistance of the speakers from the connector at the back of the radio?
The radio is easy. With the steering wheel tilted low and the gear selector in low, pull the edges of the trim around the cluster to remove it. Then there are 3 screws, 7mm that hold the radio in. Remove them and slide the radio out. Below is the speaker information.