Research,

If by "stair-step" cracking you mean that the mortar is cracking in a
stair step fashion then you are wrong that this is characteristic of
blasting. This is commonly seen in foundations with settling. The cracking
pattern in the bath room tile also sounds non specific.
If these engineers really did say that these signs are specific to
blasting then you should have no trouble in getting an engineer to inspect
your house and write an opinion. Be sure to get estimates for repairs. Armed
with this report you can then interview a few lawyers. After hiring a lawyer
follow his advice on further testing and inspections.
However, your insurer has already sent experts to examine your house.
They have concluded that you won't be able to prove a relationship between
your problems and blasting. So be aware that your experts will be contested
in court.
From your posts it sounds as if you do not want expert opinions; you want
opinions that support your beliefs. That is not a good way to resolve your
problem.

Good luck,
Dave M.