Its tough because dear, dear husband, and darling are all different, regardless husband dono should be swapped out.
This chapter where the marriage is such a big detail, dear husband is more suitable.
But later on if she continues to refer to him in that way, darling will be better.
Also....please , please don't be a harem. Just once I would like to see an isekai with a committed relationship to one woman.
Shes too pure a wolfgirl to share her man with another
If she's calling him "Danna-sama" then I'd say go with "Danna-sama" or "honored husband". ("dear husband" as another suggested would also be fine)
Husband-sama just feels too clunky, and 'darling' is too informal if she is using "Danna-sama".
Wonder when the wife's gonna find out that he murdered her brother's entire battalion. Hope her brother wasn't caught up in that too, that'd be awkward.
I think going with whatever she uses is fine like big bro= oni-chan etc. So like, it depends... Maybe 'danna-sama' like the others said but if not the darling is also ok.