You need to compute the ratio between the number of successful experiments and the number of total experiments.

If what you want to know is the probability of having the 5 guys paired with 3 men and 2 women (which is what I think the grandfather meant), the answer is

C(4,3) x C(10,2) / C(14,5) = about 9%

(number of ways to pick 3 men out of 4 x number of ways to pick 2 women out of 10 / number of ways to pick 5 people out of 14, /regardless of the order/)

If you want to know the probability of having the pairs made exactly in the order the grandfather mentioned, it's

P(4,3) x P(10,2) / P(14,5) = about 0.9%

(as above, but considering the order)

where C(M,N) and P(M,N) are the number of combinations and permutations of N items out of M, respectively.

(edit to change multiplication symbol, asterisk doesn't show)