First you have to determine who the applicant is. If the applicant is the business (non-natural person) you wouldn’t collect demographic information; whether an application is taken is dictated by your financial institutions procedures.
If the applicants are the individuals but the transaction is a business purpose transaction it is typically an exempt transaction for HMDA unless it is for home purchase, home improvement, or refinance. In this case, you can take one application with multiple applicants and if you are HMDA covered you would collect demographic information for all four individuals.