Re-Visit the Idea of Going Into Business "Together" - Hire Them as Employees

Why does there need to be any ownership at all by your sister and brother-in-law? Hire them as employees and pay them for their work. You can give bonuses for special projects associated with getting ready to open based on the skill set they bring to the table. Also, set up job descriptions with wages/salaries attached, hire them for a specific job and pay each person for the work they do. Use a formal sign-in sheet or electronic time system no matter how silly it may seem at first. If you don't take these things seriously from the start, you won't be able to get them to take it seriously when it counts.

If everyone is only going to do cleaning that's one thing. However, if one person is also going to be doing the marketing, another keeping the books and the third handling scheduling, ordering supplies, and other operational matters, then pay each person based on their primary job.

Work out an agreement AHEAD of time as to how long you will have each person in the various roles and at what point you will bring in a more skilled professional to handle a role (i.e. if you grow to a certain level of revenues/employees, handling the financial matters may require a more advanced skill set).

Be sure to set-up an organizational chart and determine how decisions will be made. These must be agreed upon before you start the business. With family members, it's going to be hard enough to get everyone to stick to the agreements, even if they are signed. Don't neglect getting them in place.

If this is your idea and your financial backing, re-visit the idea of going into business "together". Hiring them may save you a lot of headaches, especially if they have never run a business or don't have any P&L (profit and loss) experience.

Hope this is helpful!