I do one other thing and that's because my house can get dry in winter, so I have them in bowls with rocks, and have water in that. I still water once per week, but I try and keep the bowls semi full for humidity
I have also heard that these plants don't like a lot of airflow (unlike most plants) and so I have them in a corner that stays pretty "flat"
@JB if you had them in a greenhouse with the air on, that may have been too much for them?? I personally like to at least know what I did "wrong" when I can't be successful with a plant.....or sometimes I've just waited too long, and its no longer important...onto the ones that I DO have luck with!