So fruits and vegetables are very important, but they are a difficult subject in some respects. You should introduce only one kind of fresh food at a time. So, say that you start with carrots (this is just an example, you can choose anything you like). Dice or blend them and sprinkle seed on top. The budgies may be wary at first of the weird new stuff in their home, but they will warm to it eventually. When the budgies scoff the stuff down as soon as you put it in the cage, you are ready to add another new food. In a few months, you will be able to choose from a variety of things they like to eat. You can give them as many kinds of flora at once as you want, but few of us have the time and energy to do more than two or three types in a day. When your birds are eating a large variety of foods in general, you can do different blends each day to insure they are having a varied enough diet. Like, pineapple/carrot/peas on the plate one day and broccoli/squash/strawberry the next.
Also, you needen't give anything close to so much. In general the diced fruit and veg i give to my two budgies and one cockatiel take up less than a quarter cup. You will be throwing out 95% of the food if you serve so much. Start tiny: a table spoon or two and see how much fresh fruit and veg your birds will eat. If they polish off one table spoon a day, then move to two or three or more until you have some small amount of leftovers on a regular basis. Then, you know exactly what to provide!
In general, I find it best to give them fresh fruit and veg in the morning before giving them the bulk of their seed for the day. Ideally you would want it to sit for about 3-4 hours once in the day and then take it out and give them their regular food. Still, don't sweat things too much. If fresh foods stay a little longer, or even for a day, you don't need to freak out. You do need to make sure it is out by bed time. this is to prevent it going off and making the birds ill. Still, we can't all be perfect. Focus on bird keeping as a pleasurable experience, and just try to keep loosely within the guidelines