It would be helpful if we had more information on what the taxpayers are doing that they call "adult foster care."  Those payments are almost always taxable, if what is meant is "a type of long-term care arrangement where adults who need assistance with daily living activities receive support in a home-like environment, often with a focus on personalized care and community integration." 

If that's what is involved, do you count just the bedroom(s) assigned to patient(s), or do you follow the rules for daycare?  Code Section 280A doesn't limit them to children.  They apply to a "taxpayer’s trade or business of providing day care for children, for individuals who have attained age 65, or for individuals who are physically or mentally incapable of caring for themselves."