Treat that as a budgeting question with an evidentiary side. Money the family draws for rent, schooling and groceries is not capital working in the business, so a plan that quietly funds a year of living from the enterprise's peak-season cash should be stated openly and tested against what the business actually needs to keep operating.
Give the household its own reserve line
Write a separate household budget covering the low months, funded from resources that are not counted as the investment. If a spouse expects to work, note that a qualifying E spouse is generally employment-authorized incident to valid status, subject to confirming the actual E-2S notation or I-94 evidence an employer will ask for; children admitted as dependents get no work authorization from that status. Neither should be assumed as the family's off-season income.
Set the household question out as a separate document from the business plan, with its own income sources and its own reserve. That separation is useful for two reasons: it keeps personal drawings visible rather than buried in an operating account, and it makes the non-marginality discussion easier because the business figures are not carrying an undisclosed household load. Note also that E-2 is a nonimmigrant category conferring no permanent residence, so schooling, longer-term housing and any plan that depends on remaining indefinitely need their own analysis rather than an assumption that the status will simply continue.