Generally not when the seller's note is secured on the business's own assets, because that money is not at risk to the investor. Their own cash and any loan secured on their personal property do count. The car wash must also be actively directed and not marginal.
The security clause decides whether the money is yours
Treaty-investor rules ask whether the investor has placed his or her own capital at risk in the enterprise. Money borrowed against the enterprise's assets fails that test: if the business collapses, the seller repossesses the equipment and the investor's loss is limited to what he actually put in. Money borrowed against the couple's house passes it, because they must repay from their own resources whether or not the car wash survives.
The purchase can still close with a seller note; the note simply drops out of the investment calculation, and the remaining cash and home-secured funds are what get measured for substantiality. Ask the seller's lawyer for the draft note and security agreement early and read the collateral description word by word. Then confirm the couple will run the business day to day, since a semi-automatic operation invites the objection that the investors are passive, and show through payroll and projections that it supports more than their own living.