I've created some new views and a test page, to make my suggested approach more clear:
1. The test page's name is 'Test page from TS support' and you'll find the output of the 3 new views on this page:
2. The view 'parentevents-new' is set to extract Post IDs (only) for the 'Events' that we need. It has the same query filters as you added in your view 'parentevents', but the only difference is that I've structured its output to only return the comma-separated list of the post IDs.
3. The view 'Singleton Sites-new' is set to extract Post IDs (only) for the 'Sites' that we need. It has the same query filters as you added in your view 'Singleton Sites', but the only difference is that I've structured its output to only return the comma-separated list of the post IDs.
4. The view 'CombinedPlaceView-new' is the one that consolidates the IDs coming from these two views, and limits the results to only those IDs.
Please note how I've used the shortcodes of the other two views, as the shortcode attribute value for 'ids' attribute: