Charging two or more devices on the one and the same charger

If the charger is designed to charge two devices at once, ie. two or more charging ports, then yes, it will be fine to charge multiple devices on that charger.

Yes, you can charge both phones with the same power adaptor … just one phone at a time.

You don’t need a separate power adaptor for each device.

This may help you understand --> When to charge your iPhone or iPad - Apple Community

To me, your first post read as if you were asking about using the same charger to charge two different phones at the same time.

Maybe you are really asking if it is OK to use the same charger to charge two different phones......not at the same time but at different times?

If that is what you really are asking, the answer is "yes".