Grounding everything - safely
It really should be fixed properly, not just bodged, but...


Anything that's not double-insulated.  Especially anything that heats water, or which has a switched-mode power supply.
Get a proper kit from an electrical supplier, designed for the purpose.
A fat copper wire.
As far as it will go.
No.  If your appliances are "killed", they were faulty already.
I'll leave that up to you.  It's not going to be easy without another ground reference, and you don't want to introduce dangerous voltages into the system as part of the testing.