What you want to do is an digital version of Hawala. Hawala works, but there is a reason it is not automated. You can not scale it and it gets very easy to hit liquidity bottlenecks.
I think your ideas are in the right place (if you look at Raiden's off-chain side payment channels, it works somewhat similarly with what you are attempting to design) but can we agree to the fact that if they were feasible to be done without BFT mechanisms, it would have been done already? It is not like people want to use blockchains.