Since late Mendix 9 versions, it is also possible to use multiple page parameters. This could be very helpful in the scenario you're describing here. To use this feature, you can do something like this:

- Create an open page microflow in which you create the 2 objects of two different entities

- Create a page with two main DataViews with corresponding entity types
- Use an Open Page action in the microflow you created. Here you should see two input parameters

Hopefully, this will make your life easier. Using a non-persistent helper entity as Gerrit explains was (and sometimes is) a common solution as well.

Hi Felix,

Is this a temporary View of the object? If yes, I would create a non-persistent entity with the Data you want from both entities you want to show. (“Combining” two Data views into one is nothing I saw so far)
You then create a microflow to create an entity of the ( “combined”) non-persistent entity, fill it with the Data you want and use it in your data View. (via page parameter or DataSource)
If you edit the Data, there would be the need to make this data go into the correct places afterwards. 
Depending on the version of Mendix you are using, there is different options for that.