STEL2515

[beanpole]

19A
Milkmaids in song and Santa's 5 (=Reindeer)
?C?E??

20d
Waits at Christmas for example for some birds(7)
??N?E?S

Singers ???

[Lie-in King]

19a Octets - ♫8 maids-a-milking♫ & 8 reindeer
20d Singers -

"wait - (in plural) people who welcome in Christmas by playing or singing out of doors at night;
a member of a Christmas band or town band of waits..."

[beanpole]

Thank you Lie-In King

I don't think 19a is a good clue but that is typical STEL