It is expected that while on a 'temporary work assignment' you will have to pay expenses where your temporary assignment is, and also to continue to pay expenses at your 'tax home' (hence the 'duplicate expenses' requirement).
It doesn't matter what the expenses are that you pay at your parents home (you don't have to report those), just that their home qualifies as your 'tax home'.
In addition to the details provided by @BillM223, here's more info on What Is a Tax Home?
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