Cartridge Family vs Ancient Copper

How close are they?

ΔE 18.3, loose: different enough that you should pick on purpose. Ancient Copper is noticeably darker, more saturated than Cartridge Family.

Can I use Ancient Copper instead of Cartridge Family?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Ancient Copper is noticeably darker, more saturated than Cartridge Family.

Can I use Cartridge Family instead of Ancient Copper?

The same difference applies the other way round: Cartridge Family is noticeably lighter, more muted.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.