Try to have one male and two females, your chances will be better that way too, and then one female won't get harassed the whole time. Driftwood or bogwood is a big neccessary for bristlenose, they need it to aid in digestion. I found my males to be at the 7 cm mark to start chasing the females around and cleaning out small spots and the females so far has been small I had one at four cm be a mum but most at about 5cm. I had two stones very tight to each other but with a slight gap inbetween and the male would dig a hole underneath it and then chase the female in there, they like it to be a very tight spot, they feel that they can protect the eggs easier and keep the young together easier, so the smaller the caves the better, I wish you all the luck, but its really up to them