Two strokes have problems with sitting. If they sat too long, the seals that separate the working chamber from the outside of the case harden and leak.
Check for how much play the main rod bearing has, the manual will tell you what is acceptable. The little end of the rod usually has a roller bearing which is easily replaced.
Check for cylinder scuffing from people who think the less amount of 2cycle oil you use the better it’ll run which is B.S. Use what they recommend and carry a spare plug or two with you, better a fouled plug than grenaded engine.
Hopefully the engines have never had cox fuel run through them, they’ll run like a bat outta hell, for a while and smell like a model engine running.
You can take the cylinder off easily or look through the exhaust port to see if there’s any scuffing on the piston. I think Yamies use a reed valve which can crack and cause problems or break sending the pieces into the engine but they’re easy to replace and not expensive.
If the price is right, they fire up and run well, who cares about the engines? Every running two stroke failure I’ve had was due to scuffing of the pistons and cylinders and it’s easy to bore the cylinder and get an oversize piston, just make sure the machine shop bevels the transfer ports in the cylinder.
The other failure I’ve had was an Rd350 that sat and its crank seals dried up and cracked. It ran (after being towed) but it sucked in the regular gear oil which is a good indicator you need to get the crank rebuilt which was easy to get done in the 70s. Since yours are from around 2002, I wouldn’t worry about parts and if you’ve never rebuilt an engine, a two stroke is easy, just make sure you put the piston ring gap in the pin in the ring land or you’ll have a bad day.
How many hours are on them now ?
The most effective and accurate way to tell if an engine needs a rebuild is a compression test. Hour meters are good for preventive maintenance, but actual wear and tear can happen at differing rates to identical machines doing identical service, even if they are running the same fuel mix.
Compression tests and overall cleanliness/condition of the engine, engine space and entire machine will tell you better than an hours meter.
JMHO, YMMV. I was a small engine mechanic for 20 odd years.
I put 1200 hours on a Rotax using Redline synthetic oil. Normally half that time would be excellent.
I was looking at one to convert to electric, but the more I researched it the less practical it was, because everyone I found with a bad engine had a bad pump too.
If they have been run every year (takes care of the dried out seal issue), figure 700 to 1000 hours for a fresh water run PWC. YMMV, but this is what has been recommended to me from a good guy, who knows his stuff. Pumps are another matter. Sand and/or debris can do a fair amount ($$$) of damage. Also try to rock the engines back and forth. If the motor mounts are gone (common) figure on more $$$ for pump rebuilds. If the motor can move, it won’t align the pump and you will be buying pump shaft and seals for sure.