Why don't you first try disconnecting the cooker hood by turning off at the wall switch you mention. This should be a double pole switch, which should electrically disconnect it from it's supply. If the fault not longer manifest itself, then you could start looking at having the appliance tested for faults.
This does not explain why the hood on circuit 4, is tripping circuits 5 & 6. Sometimes with the best or worse intentions, kitchen fitters deputise themselves as electricians, and can make a right hash of things, this of course is not true of all kitchen fitter electricians. If, as it already has been suggested, these circuits have been cross connected, may be one possible line of inspection.
I note that your fuse board is populated with MEM ALB321 mcb's. I don't believe you could purchase an MEM ALB321 RCBO (Residual Current Breaker with Overcurrent)? You can however, I'm told, convert them to an RCBO, using a field fit RCD Pod. MEM are no more, but spares are obtainable from EATON, well not spares but replacements. Clutching at straws, perhaps these kits have not be assembled as per manufacturers instructions?
You seem to have some confidence & trust in the electrician who originally rewired your property. Why don't you see if he/she will come back and investigate these faults?
It is difficult to carry out fault finding from afar. The label on your fuse board suggest you are due an inspection anyway.