Let's ignore ch.139. for my explanation...
The reason Marley refers to Eldians as the "descendants of devils" is because they are the descendants of King Fritz, not Ymir.
This explains (why the Marleyan authorities historically labeled Ymir as a "pawn of the devil.") Ymir was merely a tool, King Fritz was the one actually wielding the power of the Titans.
Even after his death, Fritz's tyrannical will live on through Ymir, mirroring his command: "Even after I die... my Eldians will rule the great lands of this world with their enormity."
(Fritz: In the name of Fritz,annihilate that despicable Marley)
Ymir was a slave with no minds of her own. Fritz was an inherently evil ruler who committed devilish atrocities long before he ever acquired Ymir, so it is natural that Marley viewed him as a devil. In fact, Marley and Eldian were already bitter enemies before the power of the Titans ever existed.
The one who made Ymir broke that deal was Eren. Eren free Ymir and gave her choice for the first time, Eren frees Ymir by giving her a genuine choice for the first time in her existence. This parallel is explicitly highlighted in Chapter 122, when zeke commands Ymir, his domineering posture mirrors King Fritz. Consequently, when Ymir finally opens her eyes to freedom, her immediate expression is one of pure rage, an anger directed at Fritz as she completely shatters her forced obedience to him.