In OP's examples, most likely the second who (a relative pronoun which could be replaced by that) would be "deleted" (not uttered) by many if not most native speakers, if only on the grounds of "elegance".
But if we consider another example of the general construction...
1: Who does John know would want to kill him?
2a: Who does John know that would want to kill him?
2b: Who does John know who would want to kill him?
...it should be obvious that #1 asks which people John thinks might want to kill him, whereas #2 asks which (of all the people John knows) the speaker and her audience think might want to kill John. (It's entirely a matter of stylistic choice whether to use that or who in OP's example #2 and my #2a/b.)
Thus in some contexts, the second "relativiser" can safely be "deleted" without affecting or obscuring the meaning. But in others it can't, so it will normally be present or absent according to the intended sense.