I see similar questions to this one, but mine is slightly different, so here goes:
I live in Seattle, where the winters are mild, with days in the 40s°F (4-10°C) and nights in the low 30s°F (around -1°C) at worst. I live in an 8-bedroom house with all bedrooms occupied (tenants). The house has no outer wall insulation at all, but windows are double-pane and we have checked for and fixed drafts. I have a newer heat pump tied to an electric furnace, also newer.
I prefer a house at 64°F (18°), but my tenants are all comfortable at mid-70s°F (24°C) and I have argued to no avail. My heating bill is way too high for me now. What I am left with is the choice between turning the house up to 74°F (23°C) or so, or keeping it at 68°F (20°C) and buying them new space heaters with adjustable thermostats (they all have older ones now with no thermostats). They already turn the heaters off when they are not home. I see lots of good science on this site, although most of it is over my head, but I can understand the basics. Should I heat the whole house or trust the space heaters?