Grandparents won’t let me and fiancé see his father in a assisted living facility

Either he is in assisted living or a nursing home, not both.  No one's Social Security is enough to pay for an assisted living facility or a nursing home.  Perhaps your fiance's father is in a nursing home being paid for by his Social Security and Medicaid. In any event, neither you nor your finance have visitation rights BUT his father has the right to have anyone he wants call or visit him, as long as those people have not abused, neglected or exploited him (and may do so again.) Facilities often confuse the point of contact (apparently the grandparents) as people with authority to exclude visitors. But that may not be the problem.  During the pandemic, nursing homes are allowed to exclude all but a designated "essential caregiver." Please clarify the situation.