My main house has a steady amount of 850k that neither really increases or decreases. I just always end up there. :/ It's old money that raised several children and 4 generations, so no matter what I do it always ends up around there. xD
I planned on making a bakery for them as a money sink but I didn't have a lot to build it on :(
The three elders that live there have shrewd and frugal, and since those traits stack, their house bills aren't expensive and they receive about 33-35k from investments each.
With all that money, I use it to renovate their house, or I "send money to relatives" who seem to drain their funds way too fast or for when I wanna renovate their house. The latter function is available via MC Command, but you can easily just deduct from one house then add to the other via cheats too.
All I know is that once those three die and I don't give frugal and shrewd to anyone else in that house, it'll be about... The later adult years of the second eldest kid in the house when they'll naturally run out of money so I'll just wait for that to happen LOL
Hooray for bills and expensive houses!