On the tires mismatch, what are the tire sizes front vs. rear, and approx how much tread is gone on front vs. rear? How long since you put those tires on?

In general, you've got a ton of weird things going on that could have many different causes. But some things are simpler, like tire pressure being low. I'd focus on the easiest problems, because when you find the answer to that, it might end up fixing everything.

On your car, do tire warnings come from pressure sensors in each tire, or is it based on measuring wheel rotation?

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2001 X5 3.0i, 203k miles, AT, owned since 2014