Yes, you can offer them pinheads, and even small mealworms. i found they preferred the flies. Once they get big enough, I offered larger crickets, larger flies, mealworms, zophobas, butterworms, silkworms, wc moths, wc grasshoppers, etc.
Dont forget to mist LIGHTLY now and then.
If you offer enough flies and such, they are less likely to prey on each other. I kept in aqauriums and critter keepers and glass jars etc to the total of 50 different "houses". In the larger aquariums I was able to keep up to 5 together, so long as I offered plenty of food. I was keeping some as pets and wanted most for the greenhouse, but I did offer ones that didnt moult well to the chameleons, until they got big enough to fight back (and then I just let their brothers and sisters eat them).
And beware that when they first hatch they can go through screen if its not fine enough! If fruit flies can escape so can little mantids.