From the history you are saying, it is highly likely that his health history was hidden. While you may blame the agent, your uncle would have signed the insurance form. If he signed on a blank form or where the existing health issues were mentioned as None, be rest assured that even if you go to courts, the claim would be rejected. While I empathise with the family background, this ignorance may cost them badly.
It is sad to see that agents do this for fulfilling their targets. We specialise in such insurances and we ensure the disclosures are to the last level. It often irritates our clients. At times the policy application gets rejected. At times with higher premium. But we then are at peace that now the insurers have no way to reject.