If there is really no signature of the applicant and the insured, then the contract is really not established. But the insurance company said it was signed by your relatives, and they didn't know. Your passport is very useful here. The agent has never even met the insured and the insured, so the insurer failed to ensure the insured and the insured's right to know. At this time, the policy is invalid and you can ask for a refund of the premium.
But your mother has paid the premium for several years. This is another question. After paying the premium, the opposing lawyer can claim that this means that your family acquiesced in the validity of the contract. This is where the lawyers of both sides argue. But you have a better chance of winning.
But remember, if your relatives really go to court, your premium may come back, but your relatives must cooperate. At the same time, the insurance company may counterclaim your relatives for fraud. Of course, the insurance companies here are almost impossible to win, but they may just do it to disgust you. At the same time, because this case is still controversial (mainly because your mother has lost money for several years), it is likely to drag on for a long time. Do you have time and energy?
So if the amount is huge, forget it. Forget it.