Because the qualifying amount must come from your own net entitlement, after your sibling's half, mortgage payoff, selling costs and taxes actually deducted from those proceeds; taxes paid using other resources do not automatically reduce that contribution. Professional fees and project administrative charges are additional to the investment. A payment labelled as an administrative fee does not by itself count toward qualifying capital.
Work from the net figure forward
Take a hypothetical closing that clears the mortgage and pays the notary and agent; each half then reflects a smaller figure than the sale price. If one project cannot support the US$800,000 basis, that alone does not mean US$1,050,000 is your only option — another qualifying basis may be available. Written quotes for professional work exist; ask for scope, exclusions and payment timing in writing.
Prepare a sources-and-uses ledger that separates invested capital, administration charges, legal or appraisal expenses, and government filing fees. Confirm the current applicable threshold and the actual capital-at-risk treatment rather than using a combined budget as the answer. Budget for the later conditional-residence period and its Form I-829 evidence cycle without treating operating costs as government charges.