Those don't look like they're in pots and still seem to be growing okay. I've found on my Ficus that epiphytes don't do as well as on some other trees. I've suspected that the Ficus might put roots around the roots of the epiphytes and starve them, though not totally. A Staghorn Fern is an ideal home for Ficus roots to settle into, might be that's your problem. You could check, Ficus roots look very different to Staghorn roots.

The culture of each banyan tree will vary based on the solar exposure. You can't decide where to put orchids as if you are decorating your house. Most orchids are sun loving. Many like dappled light and some like shade. So study each area that may grow orchids then match the correct orchid for that particular location. And that requires significant knowledge. And that is why I previously suggested joining your local orchid society. That way you will be able to jump immediately ahead of your own limited knowledge on the subject. It is not rocket science but it does take time to figure things out. Those answers come quicker from those who have been down that path.

Map out the various solar exposures you have available for orchids. Indicate the exposure. Like morning, noon, or afternoon sun. Or all day. And how many hours.

Start plants mounted on cork bark on a back porch or a nursery like environment. Get them well established on the cork. Then next spring place them on your pre-determined spots. You want plants that will tolerate the lowest temperature recorded in your area in the last 5 years.

Study the brassavola orchid. the species and hybrids. The species nicknamed lady of the night, has a pleasant and spicy aroma at night only. There are many hybrids that are colorful. The brassavola is at home in W. Palm Beach. Not natural to PB but is happy there. It will adapt and survive the extremes once established.

Good luck

Harvey.... very well said

Thanks Ben!