From the statement that the product of their ages is 36 the possibilities of the three individual ages are:

1,1,36 (addition sum=38)

1,2,18 (addition sum=21)

1,3,12 (addition sum=16)

1,4,9 (addition sum=14)

1,6,6 (addition sum=13)

2,2,9 (addition sum=13)

2,3,6 (addition sum=11)

3,3,4 (addition sum=10)

From the statement that the sum equals the house number it is possible to eliminate all but two possibilities, because the sums of the rest are unique and would allow for an immediate answer. so you need the ones which have identical answers to necessitate the final clue. The two remaining possibilities are 2, 2, and 9; or 1, 6, and 6. (which both add up to 13)

After the clue that the oldest has red hair you can eliminate ~~1, 6, and 6~~ because the oldest two have the same age thus there would be no single oldest son. The only remaining posibility is 2, 2, and 9.