A lot of birds have issues with changing over to pellets and you are correct in not taking away the seeds. You can try fruit blend Zupreem. You can also grind the pellets and mix it with the seeds. As to the fruit and veggies, try chopping them very fine and sprinkling some seed on top to see if they will pick at the seed and potentially tasting the fruit/veggies. It’s a work in progress to get birds onto a healthy diet if they haven’t been abundance weaned.
How is the settling/taming coming along?