Welcome to group therapy.
First remove the spark plugs, squirt some oil down the bores and try to turn the engine by hand.
Drain the fuel, also from the carbs, fill some fresh fuel. Wait a few minutes and check for leaks. If no leaks, change the engine oil ( unless you want to do a full engine rebuild, then i would not bother now), connect a good battery and try to start it.
You might be lucky. Seven years ago I was given a GS1000 which had been standing for 10 years, i did as described and it started.
Only after you know the engine runs, fix the brakes etc.