Keep two budgets. The enterprise budget covers capital actually committed and at risk, plus operating costs; the household budget covers living expenses, travel, schooling and professional fees. Mixing them can make the investment look larger than it is and can hide how long the family can sustain itself.
Do not count living money as invested capital
Funds reserved for rent, groceries and tuition are not committed to the enterprise, and treating them as investment weakens both the case and the plan. Set out separately what has been spent, what is contractually committed, and what is merely available. Confirm current government fees at the time of each step rather than relying on figures quoted earlier, and ask which professional services are inside or outside any quoted scope.
Give each budget line an owner and a document. Rent has a lease, equipment has an invoice, professional services have an engagement letter, and anything without a document is an estimate that should be labelled as one. Review the two budgets together once a month during preparation, because money quietly migrates from the household column into the business column as a purchase becomes urgent, and the investor is often the last to notice.
Where a family member is contributing funds, record the terms in writing before the transfer rather than afterwards, since the arrangement will have to be explained as it was, not as it was later understood.