What you may need to do to ensure your father-in-law’s well-being is to get a conservatorship, sometimes called an adult guardianship.
This arrangement gives a person the legal right to
make necessary decisions on behalf of another adult who cannot live independently. It would allow the person to oversee or personally be responsible for your father-in-law’s care, custody, and control.
But laws in every locale provide specific criteria for evaluating whether a person qualifies for a guardianship--and this legal arrangement requires some paperwork and a court hearing. The person seeking to be appointed conservator will have to explain why he or she is the best person for the job. And surviving family members will be notified about the procedure and may contest it. It will be up to the court to decide whether it is the best route to pursue.
Whether you or yours will need to hire an attorney for help with this process depends on the set-up of your local probate court; they vary wildly. Courts in some places have established some very good self-help centers that provide necessary forms and instructions for how to complete and file them. Find out by doing a search of your city or county and the words "conservatorship" or "guardianship."
If your court does not provide good help, or the idea of going it alone just seems too overwhelming, you should be able to get referrals for experienced legal help through the local or state bar association.