The laws vary so much by state that any advice given here is not likely to be useful as far as specifics. Here in Texas, either a police officer can evaluate that someone is at risk of harming themselves or others and issue an emergency detention, compelling a psychiatric evaluation, or an outpatient doctor can write a certificate of medical examination and a family/outpatient team can file an order of protective custody directly with the county court, which a judge has to accept and sign. The specific criteria you can use for either of these varies by state, as does the process.

Elsewhere I read you’re concerned about your loved one’s delusional thinking, which unfortunately is not likely to meet the threshold for involuntary treatment without significant behavioral issues. The best thing for you to do right now is to take care of yourself, recognizing you and your boundaries are the only thing you have control over. Maybe check if you have a local NAMI chapter and see if they have a family support group. I guarantee you there are people there who have been through similar experiences.