There’s a YouTube channel Midwest Magic Cleaning that does cleanups for hoarder houses, and generally has a lot of information about hoarding disorder.

Forcing a cleanup without the permission from the hoarder(s) can actually cause the hoarding to get worse, as it spikes the anxiety and lack of a feeling of control from the hoarder. And their response is typically, more hoarding

This is a tricky situation, and typically you need therapy to address the underlying mental illness before cleanup can take place