It sounds like you are doing a wonderful job with them already. The biggest piece of advice I have is to be patient. Sugar glider personalities are all different. I've had my girl for almost a year now and while she has warmed up a TON and trusts me a lot, she is still not a huge fan of being around people. My boy, however, is my baby. He will sit with me forever and loves being close to me. The level of bond that you have with them will be determine in part by their personalities and preferences.
You can give them lots of treats from your hands - they will associate you with yumminess! Talk to them. Let them hear your voice and get used to it.
Sugar gliders bond very tightly by scent - if you put little pieces of fleece in your shirt for a while (so that your smell goes on to it) and then place those with the gliders while they're sleeping, they'll get used to your smell.
Have you tried carrying them around in a bonding pouch during the day?