Underwired or bras with metal in them don't cause breast cancer. This is a theory that has been de-bunked (along with the one about antiperspirant deodorant causing breast cancer).
Many millions of women wear underwired bras and if there was a correlation between these women and breast cancer it would have been easy to find and made by experts by now.
There is a new theory about shift work (of all things) and breast cancer. I can't put a link in here but Google 'Prof Andrew Watterson Stirling University' and it will bring up info.
Diet and weight, smoking and lifestyle, and genetics are the big contributers to breast cancer. So sorry to hear about your friends - it's a hideous disease but curable if caught early enough. I hope they pull through.