AP1 and AP2 are isolated systems with different AP computers, different electric sources..... AP systems can't have any failure at same time (AP1 and AP2).
Yes they can, because I've had it. Trouble is, I can't recall the root cause (we're talking 20 or more years ago), but the regulator was wondering if the aircraft should be certified IFR capable with such a single point failure. Nothing eventuated. Contact with Australian ATSB or the CASA Moorabbin office should elicit a copy of the incident report.