Individual I-1 and I-2 have a total of 6 children.
From the pedigree, you can see that there is a conjugal line connecting the individuals I-1 and I-2. This means that they are married. The line joining the conjugal line perpendicularly shows the next generation.
Thus, the generation produced from the marriage is 6 - 3 males and 3 females. Two of the children (1 male and 1 female) from individuals I-1 and I-2 are married and already have their own children.
In summary, individuals I-1 and I-2 have a total of 6 children.