The plants are about 3 feet tall and small holes have appeared in the leaves. There does not see to be any insects on the leaves.
There are actually a few pests that like to nibble on sunflowers. Neem oil is generally effective for most insect pests. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/flowers/sunflower/sunflower-problems.htm
My giant sunflowers are huge and healthy but haven't flowered yet. What's wrong?
Your soil may be lacking phosphorus. Use a higher phosphorous fertilizer or add some bone meal to the soil around your plants.
I planted a sunflower in the spring from a seed. It sprouted and grew big and beautiful but now it looks so sad and sick. I noticed little green bugs covered on the back of the leaves. What are they and how do I get rid of them?
The little green bugs are likely aphids, which can be found in various colors. Regardless of the pest, however, you can easily treat most with neem oil. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/homemade-aphid-control-a-natural-way-to-kill-aphids.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Can I replant my sunflower from its seeds or do I have to plant new seeds in the spring time?
You can replant them from seeds saved from the plant but it's better if you wait until the next planting season to do so, unless it's warm enough where you are located.
I am growing sunflowers in my garden, and for a while they seemed to be thriving, but then the leaves started getting this white tinge to them. They are still alive but don't seem healthy. Do you know what this is?
It is likely powdery mildew. Neem oil can help. Here is more info: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
You can also find other home remedies for powdery mildew here: https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm
You helped me grow beautiful Sunflowers. Now how do I get the seeds so I can roast and eat them?
This article will help you with that:
https://www.gardeningknowhow.com/ornamental/flowers/sunflower/harvesting-sunflowers.htm
They look like they are dying. Do I cut them off at the top or do I just let them be? They are in full sun and it has rained every single day for at least 30 minutes. Some were short and some are very large, like you said, and I planned on feeding them to the birds but I see no seeds. What have I done wrong?
Not all kinds of sunflowers have the large heads that have large seeds in them. Some varieties have smaller seeds that each have a mini flower on top so it may appear that the seeds are not there. Check one of the heads and rub at the velvety substance on the face of the flower. You should find seeds below.