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Okra is immune to any of sunflowers' toxic oils. This is what makes them great companions, and one of the few that do well next to sunflowers.

Unfortunately, something else has killed your okra. Generally, being a very drought tolerant plant, overwatering will be the culprit. They prefer dry soils, where the sunflower can tolerate quite a bit more water than okra.

Your photo did not come through, so I cannot assess the damage. I would suggest a fungicide for the area, and putting more emphasis on the care of the okra, rather than sunflowers in this case. The sunflower will tolerate the conditions necessary to grow okra, but optimal conditions for sunflowers may be just a bit too wet for okra.

Here are a couple of articles that will help:

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

https://www.gardeningknowhow.com/edible/vegetables/okra/planting-okra.htm

Plants don't usually wilt from lack of fertilizer. The could be pale & not lush, but maybe they need a deeper soaking of water. We use mushroom comp in our veg garden. And it works great.

Did you have a bird feeder with sunflower seeds? That is what these look like - sunflowers.

https://www.gardeningknowhow.com/ornamental/flowers/sunflower/growing-sunflowers-in-your-garden.htm

Applying slug pellets should be done away from the garden, as it attracts them. Attracting them to the garden will mean that, along with the pellets, they will consume the plants, also.

If you have used slug pellets near your garden, or in your garden, then they are likely eating your plants, as well.

Otherwise, unless you catch the predator in the act, it will be hard to say.

I would suggest using a few forms of pest control, together. These articles will help:

https://www.gardeningknowhow.com/special/organic/what-are-organic-pesticides.htm

https://www.gardeningknowhow.com/special/organic/natural-home-pesticides-organic-garden-pest-control.htm

https://www.gardeningknowhow.com/plant-problems/pests/pesticides

Unfortunately, your photo did not come through. Some cultivars show the stripe and some do not. This depends on the cultivar that you chose.

Also, they should be fairly ripe before cutting the head. They will ripen a little, but not enough to make a difference.

This article will help you to know how and when to cut sunflower heads in the future:

https://www.gardeningknowhow.com/ornamental/flowers/sunflower/harvesting-sunflowers.htm

When you said "normal edible" sunflower seeds, do you mean you planted seeds you bought for snacking? If so, there's no way to know what to expect. It's best to buy packaged seed varieties from a seed company that will grow to the height you desire with the seed head size you desire. If you did plant packaged seeds for home growing, it sounds like the pot is too small for the large varieties. They need a 3 to 5 gallon container. The roots of a sunflower grow wide and deep. They need fertile soil and full sun - 6 to 8 hours a day. Here is more info:

https://www.gardeningknowhow.com/ornamental/flowers/sunflower/growing-the-sunflowers-as-food.htm

https://www.gardeningknowhow.com/ornamental/flowers/sunflower/planting-sunflowers.htm

https://www.gardeningknowhow.com/ornamental/flowers/sunflower/caring-for-potted-sunflowers.htm