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If the windows stopped at separate times then most likely you have two separate issues, but it's possible they could be related.
If it's a single problem then it may be a bad switch or a wiring issue, either before the switch or between the switch and windows. The most common place to find a wiring issue is in the boot between the door and body where the wiring harness runs to the body, this wiring flexes each time the door moves and can eventually break.
Since they stopped at separate times it seems more likely that you have two separate problems going on. Most inoperative widows are caused by failed window motors. The first thing I'd recommend is removing the door panels to access the motors and use a test light or voltmeter to check for power and ground when pressing the switch, if there is power and ground but the motor doesn't run then it has failed.