Chris starts to claim social security at his full retirement age (age 66). He is fully insured based on social security rule. His PIA is $2,500 per month. His wife Robin is 58 years old. She has not participated in the labor force before. They have a 30-year-old son and 14- year-old daughter , who is a full time student. Regardless of the actual family maximum benefit, how much of his Social Security benefits are available to the family members?