That is not possible in Mendix.
And to add to the answers above: In the Java programming language, for example, you don't solve this with extensions (generalizations in Mendix terms) but with interfaces. (https://docs.oracle.com/javase/tutorial/java/concepts/interface.html). Such a thing isn't possible in Mendix. By the way, you could do something like this in a database by creation views over multiple tables but that approach is probably much more advanced than what you are looking for.