Ok so you just got into jet skiing thats cool. they say a good deal is in the mind of the beholder. since you didn't say what year they were it's hard to say if was a good investment of funds. If they are not money pits then it is an ok deal.
Assuming that these are two strokes you should buy TCW-3 two stroke oil. It is supposed to be an ashless oil.
Low hours can be both good and bad depending on how & where they stored. Things can dry rot corrode real bad, rust never sleeps.
More than likely the carbs need a complete rebuild. Thats is the reason it won't open up. Take plenty of plugs with you as a fouled plug will cause terrible performance.
As far as the other ski goes take the plugs make sure you have spark. Then pour a shot of gas in each jug replace the plugs quickly and crank over. If it still doesn't fire last resort is a shot of ether in the air intake and crank don't overdue the ether. Clean the carbs in this one too.
Well good luck
Catch Ya on Flipside
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2006 RXT with RIVA STAGE THREE KIT 295 HP
2009 RXT-IS 255 HP
2008 GTX 215 HP
Land Rocket - 2003 Z06 Corvette, Chevy