they sound like good atv's
but the low use can cause running issue's(and other things, seal go dry, as to bearings and such)
and that is my point on the fuel side of things, like new atv';s tend to start fast and easy and NO need for priming a carb on them!
if your going to start them now and then I suggest driving them as well, to help lube parts, make sure there up to temp before parking them as well, so things have a time to burn off any condensation in oils
from motor to diff's!
bearings need to be turned to keep lubing all sides of them, so just idling thing sis NOT the best way to keep older low use items IMO
Tires too can dry rot from age alone!
not maybe p[art of your question, just adding some food for thought for you
I would honestly again try and find some place that sells NON ethanol fuel and drain tanks of the old/mixed fuel and or drive them and use it up and then start with new NON ethanol fuel, it just plain and simple last longer doesn't absorb water as much or fast!, you an still treat it and I would based on your low use, but I woudn;'t be using ethanol at all if I could help it, its worth the drive to go get it!
Valves being out of spec, can also again, cause starting issue's!
so they should be checked!