I agree, sounds like things are going great in your relationship.
Glider's do not like to be held onto. Some gliders will let you hold them if they're sleepy, but usually not awake. It's instinctive fear of predators that causes that, and they will be prone to bite or nip if they don't like it. Overtime, they may allow for very short durations. My Skadoosh will nip me if I hold her in my hands, but if I scoop her up to move her to another location and not holding for long, she will usually forgo the nip. My other two Ollie and Lulu may be more nippy.
My gliders, as many will crab while sleeping is being disturbed. Some gliders can or will sleep through removing the pouch or even removing them (as of read of a few cases of such) but it's normal for crabbing when you disturb their slumber, they generally do not like that. To get back to placing your hand in the pouch to retrieve them, I recommend first holding the pouch and gently rub the outside and softly speak or shush to them and wait for them to calm down, you may even begin to hear contentment noises from them, but not always. Then, place your hand in the pouch as a fist and wait for reaction, gently begin rubbing on them. If you feel you can at this point pick them up, then try, but I think a few attempts of just using your fist to rub, then gradually start opening your hand and "hug" them inside the pouch for a while to really get them comfortable with your hand. This is the stage I'm on, it takes a while for me, because I do not stick with it as I should.
Overall, biting and nipping will decrease, and maybe some cases not occur but for extreme circumstances. However the case goes by glider to glider as they all have different personalities and temperaments. My Lulu was a fierce biter, from fear and bit very hard, even drawing blood. Over time she bite less often and it's less severe. She was down to an "I don't like that" nip like Skadoosh has always been. Then we moved and my living arrangements caused a disruption on out of cage play. There has been a little set back in our relationship since. It is taking time and trying to get out of cage play going again that is beginning to improve, but since I moved again, I am having the same situation until I get more settled in and can set up their tent. It sounds like you can see the trust growing during your out of cage play with yours, it's important so try to stick with it best you can.
As for the bra, I haven't experienced that, but I've read where gliders that have gotten used to it will take to it easily. I think if you just take them while their sleepy and tuck them in, they will take back to it.
Otherwise, it really seams that you have developed quite a trusting relationship so far and that is what bonding is. Just keep up and restart what you are and were doing and you will see it grow and grow. Take the restarting easy, see how they react and do not go faster than they're ready for, they'll let you know. They may still give a nip once bonded for various reasons, but they'll have a reason and it's usually just to let you know they do not like something you are doing, react accordingly in these situations and they'll know you respect them.