Caregivers in a residential facility are covered by IWC Order #5-2001, as "personal attendants." The regular overtime laws do not apply except to the extent that hours in excess of 40 per week must be compensated at "time and a half," and the employees cannot be required to work more than 6 days in 7, except in an emergency.
Concerning sleep time, the rules are controlled by the case of Aguilar v. Association for Retarded Citizens, 234 Cal. App. 3d 21 (1991)
1. Employees who are required to live and sleep on the premises, effectively 24 hours per day, must be compensated for their on-premises sleep time, unless they agree in writing
to receive an "uninterrupted 8 hours" of sleep.
2. Employees who are not required to live and sleep on the premieses 24 hours per day, must be compensated for their on-premises sleep time, and they cannot voluntarily agree in writing to a the 8 hour exemption described in #1, above.
Based upon your stated facts, your two regular employees must be compensated for their sleep time, because even if they were to agree to the 8-hour uninterrupted sleep time, as soon as they are awakened by the elderly man, the employees are entitled to be compensated for their entire sleep period.
Concerning the relief employee, I don't have enough information to resolve the question. However, if the employee is required to sleep on the premises, and the same circumstances apply to the relief employee concerning the elderly man, then the relief employee is also required to be compensated for sleep time.
Please let me know if my answer is helpful or if I can provide further clarification or assistance.