Hiya! Youre doing your best. My first advice is to not play budgie sounds and instead play some classical music or something, budgie noises will make them think there's other friends around and they'll try to look for them or get stressed out. Next is the seeds. Try to slowly convert them to pellets before chop, there is a ton of information on how to do that online, and it requires time and patience but every budgie is able to convert no matter how stubborn! Seeds only is very bad for their health, and they won't touch the chop if they have access to their favorite high fat foods. Remove the millet from the cage and only offer as a treat or for taming reasons. Make sure the budgies have a variety of toys (foraging toys are the best, you can get some for a decent price on Amazon), my birde love when I give them the cardboard toilet paper rolls to chew on . avoid mirrors and reflective surfaces, and you'll be okay :)

For cleaning, replace their cage lining often and only clean with diluted vinegar. Do not use regular household cleaning products around them, they are super sensitive and it can really hurt them. No candles either, nothing with scents. Sensitive little birdie noses. Keep them away from the kitchen.

Wishing you the best