Not quite.
How many holidays did they have?
or
How much vacation did they have?
is this question correct?
How much holiday had they?
2 answers
It's correct, but not common.
In the U.K., it could be:
How much holiday did they have?
In the U.S., it could be:
How much vacation did they have?
In the U.K., it could be:
How much holiday did they have?
In the U.S., it could be:
How much vacation did they have?