Welcome to the forums and congratulations on your new budgies!
Usually recently purchased pet birds take some time to settle and during this time they get scared stiff and hardly move around on the cage. Once they begin to feel more comfortable, their true colours start to show, their instincts kick in and they begin to run away from us, our hands and no longer allow the petting.
However, there are rare occasions where we get an instant connection with our pet bird from the get-go and the taming and building of trust is an effortless process, I have had this happen with my special budgie boy, Leonel.
This is where reading a budgie's body language is vital during training.
From your description and given the fact your budgies are so young, it's possible they are responding well to the interaction you are having with them despite the scarce few days you have had them.
You are doing all the right things when it comes to building your budgies trust in you and it's great they willingly eat the food from your hands.
It takes time for a good foundation of trust to solidify, so keep up with the great work you are doing with them, do not force your will on them, take things at their pace, praise them a lot by using your voice in a positive and encouraging way.
I would keep your budgies housed together, the shyest of the two will increasingly get more confident especially by seeing his/her mate perfectly at ease while interacting with you.