Except that's not the framing they view the issue in. They see it as preferable to remaining financially kept on the hook and leash of the US, only to have their chain jerked and be threatened whenever they 'act out of line'.

They aren't, it's just a reserve currency, just like the EU has the euro but uses the dollar as their primary reserve currency, or maybe a country with monetary sovrainty like japan etc is a better example, this brics currency is just a reserve one

They can have something like the ECU (the predecessor of the Euro), which was a non-circulating currency. There would still be significant challenges to achieving it but at least it doesn't sound outright impossible.