Advance inheritance and impact on other beneficiaries

[dedlnr]

I really hope this is the correct category to post in, and that it's an appropriate situation for you. I administer my brother's assets. I used some of those assets to give his son, my nephew, an advance on his inheritance from my brother. Now I need to distribute the assets to all the beneficiaries, including my nephew. How do I calculate that, given the nephew has already received some of his inheritance? It appears that I could divvy up the current assets then subtract the advance from my nephew's share. Or, I could add back the advance to the current asset amount, then calculate everyone's inheritance and finally subtract the advance from my nephew's share. I get two different amounts for the other beneficiaries when using each approach. I'm concerned that the other beneficiaries get the amount they are due. This appears to be a math/business/finance dilemma to me...right?