Druid is deeply tied to both Halsin’s and Jaheira’s backstories. We are definitely getting two druids.
Yep, now multiclassing is confirmed we can make an educated guess that Jaheira will be a Fighter/Druid as she was in BG1/2, but I don't see how either she or Halsin could drop the Druid class entirely and their stories make sense. It does seem a bit weird to have two companions with druid classes when we have a limited number in total, but I'm just going to hope that when we see the game there's a good story reason having both of them rather than swapping one of them for a character with a different class.
I guess it is possible we'll be able to tailor companions' classes to something entirely different and hang whether it makes sense if we want to. I'm not sure I could bring myself to do that, though, even if the game let me.