I've noticed that when playing as them Brice and Ianmyrre have exactly the same voice as each other. It's the same for Nala and Foxwen. I'm wondering if it's supposed to be that way or a bug because when you meet them ingame when playing as a different character they have totally different, unique voices. If it is that would be sorta disappointing.

Yes, this is normal. I suppose it was enough to record all PC-dialog twice so they have a male and female voice (the mirelurk has some sort of soundeffect, making his male voice sound different).

I don't think that this is such a big deal. It makes yourself sound a little more generic which helps to identify with the character in my opinion.