Oil should only affect your alternator operation two ways, one- the belt would slip if oily, and two- the brushes would be lubricated and not contacting the slip rings. The typical Volvo/Bosch alternators are legendary for brush hop (not enough spring force) on the inner brush. Which leads to the second issue, why is the battery 10 volts? If it charges up to the nominal 12 volts with a charger, then the alternator probably needed a new regulator/brush assembly before your other repair. If not, it sounds like a shorted cell and battery replacement needed. See the FAQs for how easy it is to spend about thirty bucks and do two screws to install a new regulator usually without removing the alternator from the engine.
The A/C part of story concerns me as crunches and grinds come from internal reciprocating parts and rotating clutches usually squeak and whir. My swag is that the system may had too much liquid oil installed and oil does not compress, only pumps, so compressor suffered a hydraulic lock, hard on clutch and belts, and disastrous to compressor that can handle oil vapor with coolant gas only. Make sure the mechanic now flushes the whole system before installing new compressor as no way to tell what broke loose in compressor. To diagnose what really happened would require tearing down the bad compressor and measuring the oil, so best bet is replacing the faulty one and keeping cool.