Kernrechtsfrage
Whether the joint parental authority had to be modified due to changed circumstances and the children's welfare.
Extrahierter Entscheid
No modification was warranted; the parents' cooperation was imperfect but still sufficient, and the children's welfare was not shown to be endangered.
Extrahierte Begründung
A change of parental authority requires a material change of circumstances and a necessity grounded in the child's welfare. The lower courts could rely on the expert opinion that both parents remained capable of care and that joint authority remained the best option, with support measures preferable to transferring sole custody.