Will the oil pressure switch cause the motor not to change from 8 to 4 cylinder

Yes. My oil pressure sensor went bad last week and then my car stopped switching to 4 cylinder mode and the remote start wouldn't work either. Changed it a few days ago and now it switches to 4 and the remote start works again.

the wrong thickness oil can cause this issue. i rec seeking diag and est from your mech

Yes. It can cause issues with the AFM system. AFM will be disabled if the system sees (or thinks it sees) low oil psi. Check the wires to the switch and make sure they are not broken or shorted anywhere. If they are not, then replace the Oil PSI switch. If there are still issues after this, then you will need a scan tool (not a code scanner) for diag.