The following analysis shows that Xiao Wang's parents are normal, but both parents contain a gene; Sister Xiao Wang is an aa patient, so we can infer that her parents must have provided the pathogenic gene, so Raul's genotype is AA. Xiao Wang doesn't, so Xiao Wang's genotype may be Aa or Aa. According to the genotype of his parents, we can conclude that the probability of Xiao Wang being AA genotype is 1/3, and the probability of being AA genotype is 2/3.

If Xiao Li's parents are normal and his younger brother is albino (aa), then the probability of Xiao Li being Aa genotype is 1/3, and the probability of being AA genotype is 2/3.

Secondly, there are three possible reasons for the Aa genotype of offspring:

(1) Xiao Wang AaX Xiao Li Aa, and the offspring probability aa =1/3x2/3x1/2 =1/9.

(2) Xiao Wang AaX Xiao Li Aa, the offspring probability AA = 2/3x1/3x1/2 =1/9.

(2) Xiao Wang AaX Xiao Li Aa, the offspring probability AA = 2/3x2/3x1/2 = 4/18.

So the probability of two people having Aa children =1/9+1/9+4/18 = 4/9.