Does a guardian and POA need to have financial transparency?

My brother is caregiver for my dad who has dementia and is living in the VA. My dad's benefits are large enough to support my disabled sister. Since my father became disabled and has been living full-time in the VA for free, it's still seems there is never enough money to do the things that make life Pleasant for my disabled sister. As caregiver and POA, I'm wondering if his financial dealings on their behalf shouldn't be transparent, to me a sibling and daughter for those in his care. It's hard to even ask for a peek into finances since he keeps no paper records at all, but files everything as PDFs in the computer. It seems the money that is coming in is far greater than what I see being spent, at the same time I realize that in this day and age, expenses are often greater than they seem. If it is generally the norm to see accountability, I might not feel wrong and asking to see how the monies are spent. At the VA my dad pays nothing, and yet his benefits equate to a normal salary. In addition my sister gets SSI or something like that and a government agency also provides a small stipend to my brother for her care