What could be some of the causes for water gurgling in sinks and toilets then leaving the toilet with little water in the bowl when washing machine is spinning out?

Lack of vents or plugged vent. I would start by augering vent stack from roof to basement. One way to check if vent is plugged, take a garden hose up on roof, put it in vent, turn it on full blast and see if water rises and overflows from vent. Let us know what you find. Vent should be able to take all water from hose, if it rises at all, you have a plugged vent.