I'm probably the least knowledgeable person here. I've had my gliders for three months now but I can't believe how much they've taught me themselves.
I suspect it will take a lot more pateince with year old gliders who are not used to human touch. good grief, it took so much pateince with our babies and I didn't think the'd ever bond to us but the have.
You've been given a good resource for reading up on bonding techniques, do that and I would definately get a small tent and use that technique to get them interacting with you.
The main reason I'm responding is to tell you that in my experience holding them or even picking them up needs to wait until they've bonded to you. Before I got mine I had read someplace that even bonded gliders aren't crazy about being held and it's never a good idea to grab ahold of them from the back to pick them up. I think we had two times there was no choice when one escaped from the cage in a dangerous (to them) place and I've got scars to show for it. The first night I brought them home one of them slipped away while I was transferring them from the carrier to their new cage and we used poster boards to gently herd him back toward the cage and it worked very well with little trauma to him.
We've had them 3 months now, they stick their head out from sleeping if they hear our voices, they climb all over us and will climb onto our hand if we hold it out but they still crab and get aggressive if we pick them up. Much better to coax them onto your hand with a treat than to grab ahold of them I suspect.
And keep handfeeding them. Let them lick yogurt and their staple diet off your fingers. Part of it is that they do learn to relate that giant finger coming at them with something good but also every animal will eventually bond to an extent to it's source of food.
Best wishes.