It's all the protagonists (Geralt, Ciri, Yennefer, Dandelion) and other prominent characters from Geralt's party in the series. Plus Lytta Neyd on the cover of the stand-alone book Season of Storms.
Without having any trustworthy source for it and just going by their looks and book motifs, then:
1. "Milva" - Maria Barring
Defining attributes: the only archer among the prominent characters, forest motif.
2. Yennefer of Vengerberg
Defining attributes: the only character with violet eyes. Dark hair.
3. "Coral" - Lytta Neyd
Defining attributes: the only prominent female character from the stand-alone book Season of Storms. Red hair. Sea motif.
4. "Ciri" - Cirilla Fiona Elen Riannon
Defining attributes: ashen hair, teenager, she is the one referred to as "The Lady of the Lake".
5. Cahir Mawr Dyffryn aep Ceallach
Defining attributes: helmet with wings, armor, dark hair. Better picture here.
6. "Dandelion" - Julian Alfred Pankratz
Defining attributes: holding a lute, impractical fancy clothing.
7. Geralt of Rivia
Defining attributes: white hair, orange eyes.
8. "Regis" - Emiel Regis Rohellec Terzieff-Godefroy
Defining attributes: grey hair, alchemy/botanical motif. Long nails is a likely hint of a vampire.