Are the aforementioned oaths considered idle oaths, or do they necessitate expiation?

There is nothing upon you in either case, for the the validity of an oath depends on the intention of the one swearing it, and your intention in both cases was to swear about something true.

We advise you not to swear oaths excessively, in compliance with Allah's saying: "And guard your oaths" (Quran 5:89), and His saying: "And do not make [your oath by] Allah an obstacle against your doing good and guarding [against evil] and making peace among people" (Quran 2:224).