How to query EntryQuery for multiple sections with varying types
I'm not sure you can achieve this in one query.
The easiest solution I can think of to your problem requires 3 queries:
{% set peopleIds = craft.entries().section('people').type('Employees').ids() %}
{% set insightIds = craft.entries().section('insights').ids() %}
{% set query = craft.entries().id(peopleIds|merge(insightIds))

The first 2 queries are executed and return the ids of the matching entries. You can then create  your EntryQuery using the ids as the only criterion.