Yeah crickets are a bit pricey, especially when you have multiple pets to feed. I don't mix the generations of crickets together. Usually once the babies hatch I leave them in the incubator tub until they are about 2-3 weeks old then they go into another tub, so each group of hatchings / generation never get put together. The only time I do put generations together is when they are full grown, but usually that's just if one tub is getting low from usage.

In regards to the difference in male and female, the females have a long tube like appendage on the back that almost looks like a long straight tail. Below is an image I found online of what the females look like. Hope that helps