The 2nd clue didn't make sense to me at first either, but I think I understand it now. When it says,

`The lady replies, "Okay, here is clue number 2: If you go the house next door (points to it), the sum of their ages is the same as the house number" '

`their' refers to the lady's children. At first I thought `the sum of their ages' meant that the sum of the ages of the people next door, which confused me. But I think the clue is supposed to give you an equation of the form,

a + b + c = # of house next door

where a, b and c are the ages of the lady's children.