Though you can't escape from the law, from my point of view, the total scenario, as of now, depends upon your approach. You have not shared the location and legal status of your company.
ESI Coverage Considerations
If the work done by employees is in an accident-prone area or of a hazardous nature, you must go for ESI. But if not, you can avoid it. As stated by you, 7 are retired persons. If you exclude them, the strength will be only 8 (less than the prescribed limit).
You can hire them on a contract basis (being professional). For that, you have to engage them through a legal agreement. Their employment nature should be mentioned as expert. They will raise a monthly bill as fees for their service, and you will pay them after TDS deduction.
Please note, don't allow them any other benefits like leave, bonus, mobile reimbursement, etc. Else, they can claim all employee benefits.
Future Considerations
But this is a temporary solution. If your company grows, you have to go for ESI, EPF, etc. If your budget allows, go for that immediately.
For better controlling and regulating, seek some expert services.
Best regards.