12 year old Manish is three times as old as his brother Rajeev who must be 4 years old.
Diff in ages = 8 years.
when Rajeev will become 8 years old, Manish will be 16 yrs old and he will be twice as old as Rajeev.

Let the age of the youngest child is 'X' years.
Then the child elder than the yongest is 'X + 3' yrs
Since each have 3yrs difference upto 5 children
And given that
=> X + X+3 + X+6 + X+9 + X+12 = 50
=> 5X + 30 = 50
=> X = 4 yrs.

Let the present ages of Arun and Harish be 4x and 3x years respectively.

Then, 4x + 6 = 26 => x = 5

Harish's age = 3x = 15 years.

Let Siya's age = x

Then Riya's age = 4x

But given Riya's age = 24

=> 4x = 24 => x = 6

Hence Siya's age = 6 yrs

=> The age difference = 24 - 6 = 18 yrs.

Total age seven persons = (26 x 7)years
Total age of the first three persons and the last three persons are (19 x 3) years and (32 x 3) years respectively.
Age of the person sitting in the middle of the row = 26 x 7 - 19 x 3 - 32 x 3 = 182 - 57 - 96 = 29 years.

Anu = (Raj + 5) + 9

= Raj + 14 -------- (I)

Raj = (Renu - 4) + 7

= Renu + 3 ------- (II)

Raj's age = 19 + 3 = 22 years

After 5 years Anu's age = 22 + 14 + 5 = 41 years

Let present ages of Sushanth = w, Krish = x, Rishi = y and Rohit = z , then
w + x + y = 43 x 3 = 129 ---(i) and
w + y + z = 49 x 3 = 147 ---(ii)
Subtracting (i) from (ii), (w+y+z) - (w+x+y) = 147 - 129 , z - x = 18 ---(iii)
Given Rohit's age=z=54, so from (iii), x = 54 - 18 = 36.
Therefore, Krish age is 36 years.

Let the age of sushma be x and
the age of her son is y
Then five years before x-5=5(y-5) ...(1)
Five years hence x+5 = 3(y+5)-8 .....(2)

By soving (1) & (2), we get
5y - 15 = 3y + 7
y = 11 => x = 35

Therefore, the age of Sushma = 35 and her son = 11.

Let present ages of Sumit=w, Krishna=x, Rishabh=y and Rohit=z , then
w+x+y = 43x3 = 129 ---(i) and
w+y+z = 49x3 = 147 ---(ii)
Subtracting (i) from (ii), (w+y+z) - (w+x+y)=147 -129 , z- x =18 ---(iii)
Given Rohit's age => z = 54, so from (iii), x = 54-18 = 36