HEllo Yen, Your D granti are really nice.
Place each male with one female or two females with one male.
You can use a 10 gallon aquarium with about 6-7 inches of substrate (mixture of decayed wood and leafmold) the female granti will deposit eggs in the bottom. She will compact the substrate to form a protection for the egg. If they are too crowed they will only lay a few eggs, so try to keep a minum number of females per container.
The deeper the substrate the more eggs you will get.
The eggs take several weeks to hatch (2-3 months)
The larvae will feed on the decayed wood and the leafmold, you can leave them in the same container or you can rear them in individual containers and as they are growing the comtainers needs to be getting bigger.
good luck with them and feel free to ask any questions, I have my 3rd generation of D granti and I rear and breed several other species.
Take care
regards
Fco T