Northern Scot - Thank you in advance

[grahamr888]

11a) Be author of western ceremony (5) ?R?T?
18a) Offering impossible for teetotallers? (8) ??B?T?O?
20a) Nothing less about nothing? It's inauspicious (7) ??I?O?S
21a) Some Carib sentiment expressed by playwright (5) ?B?E?
7d) Wise half yields and formally withdraws (7) ??C?D?S
13d) Hardened to everything in the company going to America (7) C?????S

[emeritus]

21a Ibsen (Hidden in clue)

[Mamyalynne]

13 callous

[Mamyalynne]

11 write

[cupid04]

11a] write
21a] Ibsen
7d] recedes

[Euphemia]

11a write

[Mamyalynne]

18 Libation

[bibblebub]

20a) ominous

[grahamr888]

The letters for 18 and 20 have changed

18a) Offering impossible for teetotallers? (8) L?B?T?O?
20a) Nothing less about nothing? It's inauspicious (7) O?I?O?S

[cupid04]

ominous

[Psybbo]

libation

[grahamr888]

Thank you all for your help, it is much appreciated :)