Is this what you want?
SELECT (SELECT value FROM table1 WHERE table1.id_table1 = r1.id_boss) AS id_boss,
COALESCE( (SELECT value FROM table1 WHERE table1.id_table1 = r1.id_child),
(SELECT value FROM table2 WHERE table2.id_table2 = r1.id_child)
) AS child_T,
COALESCE( (SELECT value FROM table1 WHERE table1.id_table1 = r2.id_child),
(SELECT value FROM table2 WHERE table2.id_table2 = r2.id_child)
) AS child_F
FROM r_table AS r1 JOIN r_table AS r2
ON r1.id_boss = r2.id_boss AND r1.id_child <> r2.id_child AND r1.answ = 'T'
;
Test here