Hello, and welcome to the forum!
When do your conures bite? Are they territorial or do they bite when you try to pick them up? The problem should be approached in a different manner depending on the situation. If the biting is territorial, try working with your birds away from the cage or playgym, and then gradually bringing them closer to the problem area. If the biting is a result of your actions displeasing the conures, you have to figure out exactly what causes the biting in order to address the problem. I recommend target training to help stop biting. This is training a bird to gently touch the end of a stick, and you can eventually use this to get your bird to gently touch your fingers or hands without biting. Here is a link showing how to target train your birds: [ame="https://www.youtube.com/watch?v=uqtptXFyb2c"]How to Target Train Your Parrot | Parrot Training - YouTube[/ame]
As for the fresh foods, my one word of advice would be to not give up on it, no matter what. Birds often change their minds about foods frequently and seemingly without reason. One day you can offer a certain food and have it flung across the room in scorn, and the next day it will be devoured. Just keep on offering a variety of fresh foods and eventually your conures will most likely start eating them. One thing you can do to help your bird adjust to new foods is to demonstrate that they are good to eat by eating the food in front of your bird. If my caique sees me eating something, then she MUST have the food, so this method almost always works for me. You can also mix new foods in with your bird's regular diet or try placing the new food in the place where you normally put a favorite food. I usually wrap treats in paper for my caique, so if she won't eat a food, I often wrap it in paper to show her that she'll like it.
To help your birds become more comfortable with you, the most important thing (in my experience) is just to spend time with your birds. It doesn't matter what you're doing, so long as both you and your bird are comfortable and relaxed. You could just sit near the cage reading or have your bird outside the cage with you while you do something. Trick training is also a great way to build relationships with your parrots. Look up some fun tricks on the internet like waving hello or spinning in a circle and teach them to your birds. While you train, you'll build your bird's trust in you. I think target training is a great place to start, and it creates a way for you to move your birds around without having to touch them, which is particularly useful if you have a shy or untame bird.
I hope this advice helps you out, and enjoy the forum!
[ame="https://www.youtube.com/watch?v=uqtptXFyb2c"][/ame]