divide in 9 is easy.
1 splitter with 3 outputs (each getting 1/3)
split each output with another splitter into 3.
9 outputs all getting 1/3 of 1/3 (which is 1/9)
Other than that, there is rarely a good reason to "balance" production. Just make a single belt and branch of a splitter for each constuctor.
While the first constructor will get filled faster, if you have enough input, all constructors will be building at 100% within a few minutes at most.