2001 BMW X5 Mis matched Rims?

Tires and Wheels problem
2001 BMW X5 V8 Four Wheel Drive Automatic 80K m miles

I recently purchased the above car second hand. First thing I did was to take it into my local BMW garage.

I had the Self Level Suspension Incative alert.

BMW garage checked all system thoroughly and said I had no system problems/leaks. They said the problem was non-standard wheel rims had been fitted.

I checked with the previous owner who had fitted rims from a BMW 650. Rear rims are 9Jx19 and front ones 8.5Jx18.

They cannot commit and tell me if these rims are safe other than too tell me they are not standard X5 rims.

Is the car safe to drive and what size tyres should be fitted to the rims.

This is pretty worrying at the moment. The car is still in service and I get it back shortly.