So then why not throw new fuel and plug in one of them and see what happens? I consider myself a pretty good tinkerer, but unless you suspect that they are stolen, in which case I would report them, or the previous owners had a lawn care business, it doesn't seem real likely that they all died within the past year or two, so my guess would be that at least two of them have been setting there long enough that they wouldn't be worth the effort. If you wish to try, I would take a good look at them, and discard any that had a cracked or broken deck, broken wheel assemblies, etc., as some of those things are simply too costly to deal with. After that, check the engine oil; if empty, add oil, if level, okay, and if overfull, drain it and put in new, because it probably has water in the crankcase. Drain the fuel tanks, and remove the air cleaners, then inspect the tanks and carburetors for droplets clinging to the sides. Those droplets would be water, in which case I would spray the affected tanks and/or carburetors with WD40, to displace the water. Replace the spark plugs, add some fresh gas, and see what happens. So far, you'd be out $20 - $30, which probably isn't much if you think there is a chance one of them will start. And make sure that they have blades on them, because the engines will not run without one. Then, if one of them works out for you, that is the time to change the oil, replace the air filter, and sharpen the blade. As for whether or not they will do a good or bad job, you should be able to make some manner of decision by looking at the condition of the decks, wheels, and blades.