His grand parents had grown feeble and helpless.

The correct answer is A. weak.

Feeble means weak or frail, especially through old age or illness. Incapacitated means unable to function normally, especially through injury or illness. Timid means

In the context of the question, it is clear that the grandparents are no longer able to take care of themselves and need help from others. This suggests that they are weak and frail, not timid or humiliated.