Everyone on the flight can sue Air India in England and Wales regardless of where they live because the flight destination was England. That is prescribed by international aviation law (Montreal Convention).
They could also choose to claim in India or the jurisdiction where they have their principal and permanent residence provided that Air India also operates there or has a presence. No indication yet that any passengers were US resident but who knows.
The airline is liable to all passengers up to about USD 200k regardless of accident cause. Above that they can disclaim liability if they can prove they were not negligent, which they would not of course be able to do if it was a deliberate pilot act.
The amount of money a family can claim will depend on lots of variable factors such as age, number of dependants, salary etc and the quantification rules for fatal accident claims in the jurisdiction where the claim is brought. They also have the right to an immediate advance payment which has already been offered by AI excess of the statutory minimum.
It’s common for claimant lawyers to try to find a reason to sue a US-based manufacturer so they can get a jury trial and much higher compensation. Often they look not just at mainframe manufacturer but also sub-component manufacturers. A claimant in a claim v a manufacturer has to prove negligence though, unlike in a claim v an airline. This is much harder in the case of a deliberate pilot act but they could argue that the system was not sufficiently fail safe to prevent the deliberate act. See arguments against Boeing around 9/11 re Flight Deck doors not being robust enough to prevent forced entry. Personally I can’t see that working here but a lot of these claims are based on bluffing to force a settlement.
Also families of those who died on the ground or owners of property damaged on the ground will have claims against all involved under Indian law.