Alrighty, lotta questions LOL, I'll try and answer the best I can.
1: Substrate. Depends heavily on the species, Asbolus, Cryptoglossa, Ceronopus, and Edrotes will all do best on a pure sand substrate, or sand mixed with a very small amount of coco fiber/peat moss. Whereas with Eleodes it depends on the exact species, but most will lay in a 50/50 sand/coco fiber mix, and most Embaphion prefer just straight coco fiber. As for the substrate depth, at least one inch will be needed for breeding.
2: Keeping methods for larvae. Ideally you will want to be keeping each species separate, as larvae of different species will eat each other and outcompete one another. And the larvae of all Asbolus and Cryptoglossa are actually very cannibalistic towards their own siblings and need to be housed in separate deli cups from a young age if you want decent larval survival rates.
3: Food for larvae: All of these should take dog food as a staple diet (Tenebs are pretty protein hungry), and you can supplement with root vegetables and/or hardwood leaf litter. The only ones I'm unsure of are Edrotes since no one has ever bred those... But I am rearing larvae of a related genus and they take dog food just fine.
4: Leaving larvae in with adults. Not recommended for Asbolus/Cryptoglossa since the larvae are cannibalistic and actually need to be removed from the breeding container as soon as they start hatching to prevent them from eating each other. The rest of these species do fine with the larvae kept communally in the same breeding tank as the adults, though you'll have to isolate them all for pupation unless you have a very deep substrate with a vertical humidity gradient (humid at the bottom, dry on top).
5: If not, what size container to house larvae in? For Asbolus/Cryptoglossa I use 2-4 oz deli cups, which seem to be big enough to rear them to maturity in. I use the same size delis for pupating the larvae of other appropriately sized Tenebs, filled with humid compacted substrate for them to make their pupal cells in.
Hope this helps!
