Propagating succulents can feel daunting, especially if you’re not seeing results. It’s great that you’ve gotten the mother leaf to grow a rosette! Sometimes that’s the trickiest part of propagating. If the baby leaves are dying and not putting out roots, it sounds like they’re not getting enough water.
You’ll want to keep the leaves and babies on damp soil. A spray bottle is great way to mist the soil so the leaves aren’t drenched each time you water. As the water begins to evaporate from the soil, that should entice the succulent to send out some roots to draw water out from an external source instead of just getting everything from the mother leaf.
If the rosette still doesn’t have roots as the mother leaf begins to die, you’ll want to make sure the soil is consistently wet. The baby should start to “stress” once the main source of nutrients is gone and put off roots to reach the nearby water (in the soil).