You can put the pine back up on the exterior wall if you want all walls to be same.
If everything checks out on inspection and wife is still vehement about painting over pine, ( And why is that? She got it confused with naughty pine? But I never argue with a wife, anybody's wife) its possible that if you are careful in removing pine, right buyer may pay enough for drywalling and painting.
To paint the pine; First step, shake head ruefully. Wash walls real good to remove any oils and dirt. Sand entire wall, inside the coves and grooves with 180 to 220 grit to knock off gloss. Spot prime knots with two coats of white pigmented shellac, sand between coats. Better is two coats of transparent amber shellac then one coat of the white. Sand lightly after every coat, wipe off dust. Then prime entire wall with good quality oil based primer.(Zinsser) If you don't prime the spot treatments will show through as blotches. A shellac based primer will show blotches.
Let primer dry a few hours past recommendation on can. Lightly sand primer, caulk as needed, then paint with your choice oil or water based. Probably two coats, primer can be tinted to close match of final coats.