Complex sentence: Meissner contends that Hitler (though undoubtedly impressed by Magda) was an exceptionally close friend of the couple in the early days; he enjoyed staying at the Goebbels'Berlin apartment, where he could relax, and he grew very fond of the Goebbels' children.
Split into simpler sentences: Meissner contends that Hitler (though undoubtedly impressed by Magda) was an exceptionally close friend of the couple in the early days. Hitler enjoyed staying at the Goebbels'Berlin apartment, where he could relax, and he grew very fond of the Goebbels' children.