Is it obligatory to show concern for second-degree relatives (such as the children of maternal uncles and aunts, and paternal uncles and aunts, etc.), or is concern limited to ascendants (fathers and mothers, grandfathers and grandmothers, paternal uncles and paternal aunts, maternal uncles and maternal aunts) and siblings?

There is no harm in focusing on close relatives (paternal uncles, paternal aunts, maternal uncles, and maternal aunts) without their children. Maintaining ties is obligatory for those within the prohibited degrees of kinship (mahram), and commendable for those who are not mahram, such as their children. Maintaining ties of kinship is not limited to visiting; rather, it is achieved through communication, correspondence, greetings, and anything that is customarily considered a connection.