Actually, there is no need to have maxTotalHumans and maxTotalPets add up to exactly maxTotalSims.
The EA settings don't do that either. They say
Code:
uintprop maxTotalSims 10
uintprop maxTotalHumans 8
uintprop maxTotalPets 6
Which means that you can have no more than 8 humans, and no more than 6 pets, but the grand total must not exceed 10.
So if you want, you can give yourself more freedom by using settings like
Code:
uintprop maxTotalSims 200
uintprop maxTotalHumans 200
uintprop maxTotalPets 199
Which means that you could have either 200 human sims, or one sim and 199 pets, or any combo in between that adds up to 200.
And any other set of numbers is also ok.