We rent a house with a septic system.
Lately we have noticed our toilets bubbling and the water level getting very low in the bowl when the shower or bath tubs are draining. Is this a sign our septic is not functioning properly? Would pumping the septic tank help? What other concerns should I have?

Sounds to me like you have a vent problem or a blocked drain if you have plumbing on higher floors... when the shower drains its creating a vacuum the vent isn't relieving and so its siphoning water from the toilet bowl .