Ok lets take a deep breath ...
First, approx how old are the gliders?
What exactly have you tried feeding them, itemized, list everything.
Corn IS part of at least one diet, bml so saying don't give corn isn't always accurate.
Lots of things can contribute to gliders not eating well.
How it's cut ( to big, to small ) , how it's served, deep dish or shallow plate, location of the plate or dish in the cage ( on the floor or on the cage wall up higher, under a wheel or toy etc. ) age, over feeding ( to much food on the plate) , giving to many snacks, offering filling drinks during the day, the moon, the weather, in heat, room temperature, keeping the lights on late at night so they don't come out of the pouch for long amounts of time, new environment ( home, cage , people, smells )
I'm sure I could come up with more but I think you get the idea.
critter love and bml are NOT "vet approved diets" They are diets that have been around long term, and have gone through some testing, that many people feed. In fact one vet I saw told me my gliders would be malnourished if fed bml she suggested a pellet diet. Obviously I know differently and my gliders are far from malnourished which she saw when she finally got my girl out of the pouch and saw that she is a hefty 180-190 gram glider
we had a heated discussion about diets that day and I was not impressed with her lack of knowledge and scare tactics she tried to use on me.
Vets are not dietitians and if they endorse a diet for gliders it's because they were either paid to by the manufacturer or that is that the only information they have.
Byk may not have said it in a delicate fashion
but he is right a healthy glider will not intentionally starve themselves if there is edible food available. If they aren't eating or eating much there is likely a reason for it, you just need to find the reason and fix it.
Another thing to check is the food itself, they maybe eating more than you realize. Most veg they will only eat the tender middles and leave the shell intact, like peas for instance, check them they maybe hollowed out but visibley look untouched. They don't eat the skins because they can't digest the insoluble fiber.
Getting on one of the widely used diets is important, since your gliders love corn, bml would be a good choice for them. It's easy to make and corn is on the allowed list of fruits and veg that is fed with bml. Serving size per glider is under the recipe on the bml site. It's a straight forward , easy to make, affordable to feed consistently diet which takes ALL the guess work out of what to feed. All you have to do is follow the directions exactly.
It may take the gliders a few days to start eating it well, and thats ok.
I feed bml, and the hefty glider I mentioned above is a corn freak, she will not leave the plate until she has consumed every piece of corn on it. My boyfriend thought she wouldn't eat any other vegetables until I showed him that she does. She is also a sweat pea addict, if there isn't corn on the plate that is her next fav. He just couldn't tell that she was actually eating them because they looked intact.
Feeding and diets are one of the most stressful things for newer owners, I know it was for me for the first 8 or 9 months until I really understood the diets. It's ok to be overwhelmed with it most people are. If you would like help choosing a diet I'd be glad to talk with you about it. I suggested bml because it's a great fit for new owners but, really it depends on your own circumstances and it always comes down to what the gliders will eat well
Personally, I tend to overfeed and put to much on the plate sometimes, when I do this ALL of my gliders eat less than they normally do. I have to physically measure out each portion to not over feed. When I measure they eat better, there is always a little left on the plate so I know they got their fill and aren't still hungry despite me not being over generous.
My gliders are also picky about how it's served and what it's served in and where it's served. I have to use shallow plates, chop fruits n veg in small cubes, one cage I have to use two plates because there is food aggression. I tried bowls and layering the fruits n veg n bml they wanted noting to do with it. Some people have to leave fruit n veg in big chunks for their gliders to eat it.
Play with it, try different plates and bowls, how you cut things, make a cut off time for day time treats no treats after 2 or 3 pm so they are hungry for their main meal when they wake up.
When are you putting their food in the cage? what time of day? when do you take it out? do they have it in the cage long enough to eat multiple times ? They don't eat it all in one sitting they eat throughout the night multiple times...
http://bmldiet.com/bml-recipe.html