ΔE 31.2, loose: different enough that you should pick on purpose. Chestnut Brown is noticeably darker, much more muted, warmer than Fairy Pink.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Chestnut Brown is noticeably darker, much more muted, warmer than Fairy Pink.
The same difference applies the other way round: Fairy Pink is noticeably lighter, much more saturated, cooler.
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.
See Fairy Pink on the colour wheel See Chestnut Brown on the colour wheel
All matches: Fairy Pink equivalents · Chestnut Brown equivalents