Unless you have a blown fuse in the engine compartment, oxygen sensors alone wouldn't cause a trans failsafe program to be activated.

Your best bet is to see exactly what kind of trouble codes are stored in the DME and EGS then check all related fuses, that is where I would start and not by spending money on oxygen sensors.

Of course if you find wires that are shorting out or frayed never a bad idea to address those issues.

It sounds like you might need to find someone that can do some proper troubleshooting. Maybe a better indie?