how do I revive 2 full tanks of gas that's been sitting since last September 91 octane or should I siphon out runnin 525sc

Speaking from just myself, I would just fire it up and run it. I also have fuel setting that long and have not had an issue with ethanol or non-ethanol gas. Have been running non-ethanol fuels for the last few years, and no issues (530hp 502)

You will NOT lose Octane. Fuel goes bad in many ways but Octane is not a problem. Run it

I wouldn't worry too much. When I had my 525SC Pantera, it wouldn't get used for 8-9 months.
In the Spring, depending on how much fuel was in the tank, I would usually just add 5-10 gallons of 110 octane to be extra safe.