Unfortunately, that cannot be done in Cassandra (at least for now).
One possible option is to change your model to something like
id | city | rue | age | family | name | siblings
----+------+-----+-------------------------------
1 | c1 | r1 | 23 | si | si | {'b', 'd'}
then you will be able to execute query:
select json city, rue from addresses where city = 'c1';
to achieve "ready-to-use" json in result:
[json]
-----------------------------
{"city": "c1", "rue": "r1"}
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