Bought 2 Yamahas 2 Stroke XL1200 and GP1200R both from 2000 and need help

I just registered with this forum and want to say hello to all. I have a lot of experience fixing cars, diagnostics, rebuilding, painted cars, worked on boats own one but HAVE NEVER OWNED OR WORKED ON A 2STROKE PERIOD. Need help, better to ask rather than waste time guessing. Have the service manuals for both 2 strokers
That said I bought 2 different Yamaha jet skis the 2000 XL1200 3 seats and the 2000 GP1200R 2 seats. Both have been sitting for awhile, so I did compression on them with a not so new and cheap tester so I will have to redo it with a better one. My tester is for automotive compression and I saw something online that said because the hose of the automotive ones is a little longer, it might read below accuracy on a 2 stroke so you can add some value to it after the reading(?!). Not in car engines you don't
- Anyhow the compression on all was 90+, only one had reading of 100. That is low I know as I have read needs to be at 115-125 for a healthy engine. When the needle gets to the 90 it quickly jerks back and forth and doesn't stay still. Kind of like when you use a vacuum tester to find leaky valves or a vacuum leak in a car. Needle is not steady. It might be the tester itself.
- So I don't want to rebuild the upper end right away if possible, I can will a USB camera through the spark plug hole and see what surprises there are
- I do want to look at the carbs maybe adjust clean or rebuild
- fix the urgent issues like the oil hoses that could brake and add adapters that prevent it got to find which
- want to know about gas and oil mixing(mine have the gas and oil separate so how do I do that, can it be premixed for a better combination where the oil mixes properly, so it doesn't build up somewhere, or is pouring them separately good, do I need to siphon the old oil out also?
- The handle bar on the XL1200 is stuck to the right side. Found the cable that goes all the way to the back from underneath the steering column I will try to spray something(blaster spay) or better off change it, if I figure out how I know how to remove the back and probably the cable underneath, but in between it goes through some areas in the battery compartment and under the motor
- The XL1200 has a cat sticker and I want to replace it with a D-plate and chip if needed, because when I started the engine there is a weird rattle in that general area, could be something else of course, also it is over ten years old actually 18. The cat might already be out, don't know yet.
- I already suctioned the gas out of the GP1200R(not the oil yet) will do the XL1200 next(can the old gas be reused for anything I have 5 gallons
- when I started the GP1200R it actually sounded better but when I accelerate white smoke comes out of the exhaust will post dropbox link to video of it, looked online and a lot of the same models do the same don't know if the same amount
- The XL1200 is not showing the same smoke just the regular blueish greyish smoke(not too much either) from the burned exhaust mixture of oil and gas.
- I bought spark plugs for both, NGK (7986) BR8ES-11 I hope they're ok for both because the XL1200 had NGL R plugs nevermind the R is on the new plugs also
I think I listed most of my concerns, sorry for the lengthy text but want to cover my bases and noticed that you guys are really great at helping. Great forum here. Thanks in advance to all.