Yeah that’s more or less my thinking. So if we assume Crown Prince Wilhelmina abdicates his headship of the Hohenzollerns, his son Louis Ferdinand is crowned King in 1949. Then his son Louis Ferdinand II after him, and then Georg Fredrich as the current king.
It is also possible that Louis Ferdinand's eldest son, Friedrich Wilhelm, could succeed him, with a different marriage or a change in the succession law.
We could reasonably assume that Wilhelm could abdicate his headship of the House, considering how OTL he withdrew from political/monarchical activities after the Night of the Long Knives/Röhm Purge and he'd later leave Potsdam for Oberstdorf for a treatment of his gall and liver problems. He may deduce that it would be better for the people to have someone younger and in healthier shape, and may even feel regret for having supported Hitler prior to his coming to power.
And yeah, since we're dealing with alternate successions, Friedrich Wilhelm could reasonably end up having a different first marriage after his father becomes king, considering that said marriage happened in the 60s. Similarly, Ludwig Hermann Alexander Chlodwig King of Hesse could also possibly have an heir after becoming King unlike OTL, though that does mean, unless another method is taken, the houses of Hesse-Darmstadt and Hesse-Kassel remain divided.