Oil loss and catalytic converter/O2 sensor check engine

We have a couple of things going on that I suspect may be inter-related.
The car is a 2001 Toyota Corolla now at 103000 miles. This car has been losing oil for the last 15000 miles or so. The rate of loss in now at a little over a quart per 1000 miles. No sign of leakage in driveway at all. It does not have a smoke trail when driving either. It is must be burning the oil even though at that rate it should be showing from the exhaust, but that is not apparent.

The second problem is the check engine lite came on indicating a catalytic converter/o2 sensor problem. We have had the converter replaced, still had check engine lite indications. Changed both the before and after O2 sensors, then the after O2 sensor again. Still the check engine lite codes telling of catalytic converter operatiing below minimum. Midas checked the converter and claims their equipment not failing yet the problem persists and operation suffering.

My question is "could the oil loss problem be causing the catalytic converter/O2 sensor problem too?"

And is the Toyota oil loss problem wide spread in that engine?

Many thanks for any insights you can shed on this.