1st: Please post questions in the appropriate forum. This is a hardware (gear) related questions and had no business in the FAQ News forum.
On-topic: The Yamaha should be able to handle a 2 Ohm load. When putting 2 speakers in parallel, the resistance will go down by half of the resistance. In your case this means that if you parallel two 8 Ohm speakers the end result is an amp load of 8/2=4 Ohm. If you add a third speaker (in parallel) you will get 8/3=2.67 Ohm.
Having said that, I would be VERY careful adding speakers with varying power ratings. You can’t run them hotter than the maximum power of the weakest link, the 200W SV12. You run a serious risk of blowing up the lower power speakers if you don’t watch your master volume.
Especially at low frequencies a 2.67 Ohm load will come close to 0 Ohm. And dance music being bass heavy, that is gonna happen a lot.
Personally I’d trade in the lot and get 4 identical active speakers from a good brand (even used) with an option to add some subs in a later stage. Looks better, most likely will sound better, be more manageable (no heavy amp to lug around or heavy speaker cables) and offers built-in redundancy (lose one speaker and still have 3 left).
Just my three cents as usual.
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