It'ss a public place and part of the coastline so I'm pretty sure it wouldn't be closed, however, I could be wrong!

There are quite a few stairs. While not steep, they are not all of timber, but some made into the ground. These ones are sloping, and I found them difficult. I have dodgy knees, and wouldn’t have contemplated going down, but Green’s pool is just so inviting. So I went, but it was extremely difficult and painful. If they can walk long distances, though, they should be alright. There are benches to sit on at various intervals. If they really want to swim at a lovely beach, but do not think they can negotiate the stairs, the beach at Ocean Beach, Denmark is still very nice, and much easier to get to.

Greens Pool is in a national park so no hotel/motel there.

It's probably best to address this question to the Shire of Denmark. There would be issues to address, like maintaining public access, public liability, parking, etc. Best to get permission in writing, with a clear understanding of what you can and cannot do.

Access to the beach is by means of well-constructed paths (with some resting seats and lookout platforms) and steps. It's well-maintained and very safe.

Yes