I'd like to add that most birds will not touch pellets as long as there are seeds in the cage, so I would recommend maybe switching them onto pellets first so they learn to recognize them as food and not ignore them after they've finished their daily seed.
Weaning budgies onto pellets can take forever and be extremely frustrating. The best way is to do it in ratios: Every time you change their food, add in a few more pellets, then a few more, then a few more (about a teaspoon more every two days) and after a week, the ratio should be at about 25-30% pellets to 70-75% seeds. At this point, they usually only ate the seeds, and then begged for more seeds, ignoring the pellets.
At this point, do not give in to their begging for more seeds. Most birds will only begin to eat pellets after there's no other option.
This seems kind of dramatic, but that was the only way my little girl learned to eat pellets, and now she loves them!
Eventually, increase the pellets until they are 50-50 with the seeds, and finally mostly pellets, then cut out seeds entirely. Budgies can go for 2 days without food, so don't worry if they don't eat. They're usually inclined to take a nibble during this time!
After a few days or so with just pellets, you can add seeds back in and offer like 1-2 tsp. of seeds separately as mentioned. I hope this helped!
I recommend Zupreem Fruitblend for it's appeal to picky eaters and convenient size (get XS size for finches) and Roudybush and Harrison's because of the quality of its products. All three of these brands are very good!
Let us know how it goes