The second batch of buds that appeared are not opening...i have seen a couple of them off the plant. I give it light, watered it, although I once read that they like to stay dry, so not too overwater...Is once a week too much?
I think the reason for the buds not blooming could be that they are exposed to extremes in temperature. Excess heat or cold will kill off buds, but maybe these cacti are more sensitive to a draft or change in temperature?
I'm not terribly sure about overwatering or underwatering, but for H. undatus, to help prepare for flowering, you let it go dry for a month or so, then water it gradually. So maybe letting the roots go a little dryer than usual would be beneficial to help induce formation of buds? For my Christmas Cactus, I give the plant a normal amount of water, and it perks up fine after or during flowering. Mine will wilt during flowering somewhat, perhaps because of the water and energy needed to keep up a flower, its fruit, or a bud. While it's flowering, probably keep the soil on the moist side.