Using multiple UNION ALL statements in WITH clause
In the recursion you want to go on with x on a y match and with y on an x match. Use CASE WHEN to check which one matches.
, rokon (x, y) AS ( SELECT x, y FROM testver UNION ALL SELECT CASE WHEN gy1.szulonek = r1.x THEN r1.y ELSE r1.x END, gy1.gyereke FROM rokon r1 JOIN gyerek gy1 ON gy1.szulonek IN (r1.x, r1.y))