His grand parents had grown feeble and helpless.

Weak : lacking the power to perform physically demanding tasks; having little physical strength or energy.
Incapacitated : deprived of strength or power; debilitated.
Timid : showing a lack of courage or confidence; easily frightened.
Humiliated : make (someone) feel ashamed and foolish by injuring their dignity and pride.
Feeble : lacking physical strength, especially as a result of age or illness.

Synonym of Feeble is Weak