-snip-
I mean before anyone could trade among these 195 you need any of those currency to be able to travel across, and if only 6 countries decides to breakout from USD how do you think it will affect the US dollar?
There will be no much effects
It still depends on a number of things. Just judge their economic strength and how much they do business with other countries. If other countries depend a lot for business on BRICS countries where some of them are known to be slowly becoming "super power" countries, then they are enough to bring influence in the de-dollarization movement.
Although these 5 countries are also another "super power country" that would conquer so easily if the de-dollarization takes effects., they are also the major export of goods and service across the nation and sure BRICS will become known but may not affect the dollar itself or that much.
For example, just as some country stopped bitcoin mining it only affects the bitcoin price for just that month or so, and after which it bounces back to normal price and i believe such scenario would likely happened to the Dollar as well.