Can Family exist with an incomplete set of composable classes, or should they all be compulsory (for example, only Husband and Wife or only Wife and Child)?
It depends on the logic of your subject area and, accordingly, the code of your application. If the application allows the existence of incomplete families, then of course it can, and if not, then no. But by itself, the use of the composition does not impose any restrictions on it.
Can an object of some of the composable classes be destroyed before the destruction of the container object, or are the composable objects required to exist as long as the container object exists? To be created not at the time of creation of the container object, but later, for example, when some condition occurs?
Here again, the restrictions are only in the subject area (and not in composition). Is it possible to change the family? Is the death of its individual members possible? Will an incomplete family be considered a family in your application?
In the family example, it is more appropriate to use aggregation and not composition. In other words, aggregated objects (family members) should be created outside the object of the aggregate (family). They must be passed to it from outside (constructors, assignment, adding an item to the collection). Accordingly, they can (and should) exist outside the object of the aggregate. But, once again, I need to focus on the subject area and its logic.
Summarizing: in a container, a container controls the life cycle of objects being composted and can create / not create / destroy / dynamically replace them depending on their logic. When the composition "container" can exist without content but the contents (family members in the examples) without the container can not and "die" with it.
