Hello, first of all welcome to the forum
your models are suffering from "zinc plague breakage".
If I say something wrong, someone correct me.
It seems that in the past (and I do not know today if this danger could be incurred or if it has been resolved) the models were built with a metal alloy that contained parts of zinc, if the zinc is in an inadequate quantity, over time runs into this phenomenon, where the models become shortcrust pastry and practically disintegrate in the hand.
Unfortunately, nothing can be done, only hope that the models (especially the 747s) are not affected by this phenomenon.
The 737, on the other hand, I don't understand the problem, as I see that the wings flex a lot upwards. But are they metal or plastic?
Sorry but I don't understand from the photos.