So 1980 Dad's age is 4(x+y).

And because 1988 dad's age is 2(x+8+y+8).

Then there is equation 4(x+y)+8 =2(x+8+y+8).

1980 The sum of the ages of brother and younger brother: x+y= 12.

Eight years have passed since 1980 to 1988. After all the brothers and sisters have doubled, we get 1988 after subtracting Dad's eight years. The increment of the sum of the two brothers' ages is 8*2*2-8=24, which is 1980.

1980 is 48 years old, so my father was born in 1980-48= 1942.