The entire thread was about accounting, then a sub-thread on family accounting, then you pop in to just say 'I do my accounting solo, as does my wife" which may be on-topic, but just not relevant.
But the intention of your parent was "when funds start to co-mingle or you get more complicated accounts" and saying "Don't co-mingle" doesn't help answer the question for those who do co-mingle and asked for help in this thread.
The entire thread was about accounting, then a sub-thread on family accounting, then you pop in to just say 'I do my accounting solo, as does my wife" which may be on-topic, but just not relevant.