@Benayla Nope, faster molting may sometimes indicate gender (males) but is by no means exclusive, and I've had females outpace males in growth too as nymphs. It can come down to many small things such as one habitat closer to a heat source (window, vent, electronic devices, etc), one had more quantity or better nutritional feeders (especially if housed together), etc that causes some individuals to grow faster.
If you plan to inbreed the nymphs from the same ooth, yes with any mantid species males die sooner than females in general. Typically females live another 2-4 months after the males are already dead from old age. Kind of a natural anti-inbreeding trait that mantids have in that regard.
There are some "tricks" to make the other nymphs catch-up in growth such as keeping the slower growing nymphs warmer (heat source or even higher on a shelf) and giving them more feeders typically. The same is true for slowing down the faster growing nymphs, keeping them colder (keeping them in a AC colder room, lower shelf) and feeding them less.
I say moving them on shelves higher or lower, as five feet of distance from the floor can vary the temperature several degrees (2-5F usually depending on the room insulation/vents/etc) - and in young nymphs enough to counter-act the gender growing trait. Be aware though such tricks are largely unsuccessful, and most be properly done and monitored to their care needs - so the nymphs are not killed by mis-care.
