The best way to house ants is to provide a gradient for humidity so they can decide where to go themselves. They know what's best for them. Even in a test tube setup I will find queens hugging the cotton and some queens halfway down the tube. For a dirt setup, just wet one side and the water will spread by itself and make a gradient.
Myrmecocystus mexicanus are fully claustral so they don't need to eat until their first workers. I couldn't get mine to accept any sugar water immediately but they accepted it about a month later after I kept offering it. I feed mine pieces of crickets, the queens don't eat it directly unlike my Pogonomyrmex colonies.
If they still aren't founding successfully despite getting brood boosted then it's probably out of your control. Things we can't control like infertility, failed genes, individual differences can all affect success. It sounds unlikely that all 5 of your queens are infertile but it is still possible. I wouldn't toss them unless they die since I have a queen that produced workers after I gave her a new test tube setup. So you can try moving them to a setup.