Ok . Have you read up on weaning by abundance?
The best practice is keep hand feeding as long as the babies want. While at the same time offering fresh veggies , some fruit, seeds and pellets.
The babies are actually willing to try more foods when they still have the safety of hand feeding. As the babies wean themselves by dropping a feeding here and there. Usually the still want the night feeding the longest. You keep offering the feeding and let them decide to refuse. You play with the veggies and other food to help them learn to eat it along the way. This is the best time to get them eating veggies, and warm mushed pellets, you want to offer lots of different foods all the time. There is a lot of wastage at this stage.
Babies can also backsliding, as they might have rejected all have feeding but now want and need them again.
Babies are going through rapid growth and mental development.
Just seeds is not going to meet their needs, and can lead to neurological problems for life as they miss vital nutrients during this critical time. It could be why they are begging for formula again.
You need to offer warm cooked veggies , chopped up tiny pieces of veggies, everything you can to get them to start eating those healthy foods as well as pellets, and the seeds.
I'm going to link so you brought home an unweaned baby. It can seem a harsh read but has good info. Research abundance weaning yourself too. I will also add some other links that I think are good.
A small cage while they are still babies is actually good, as they don't perch well yet.
http://www.parrotforums.com/breeding-raising-parrots/74363-so-you-bought-unweaned-baby.html
http://www.parrotforums.com/breeding-raising-parrots/19049-hazards-buying-unweaned-baby.html