How can an API query reference another API query?

Here is a similar scenario that should help you out.

http://datachix.com/2014/05/22/power-query-functions-some-scenarios/

Basically, the concept is to turn your API Call 2 into a function that takes one or more parameters and then you call API Call 2 function for each row in API Call 1.

In your case, you may have to create multiple functions and custom columns that call those functions, or return everything in a comma-separated return value and then do a split on that column as a subsequent step in your API Call 1 query.