They can be reconciled by either one of the following explanations:
Abdullah bin Abdul Muttalib is not a dweller of hell. The hadith (أبي وأباك في النار) can be interpreted to refer to one of the uncles of the Prophet ﷺ who received his dawah and then disbelieved in him, e.g. Abu Lahab or Abu Talib. That is because in Arabic the paternal uncle can be called أب, such as in the Quran 2:133.
The message of previous Abrahamic religion had reached Abdullah and evidence was established against him. Hence he would be among the dwellers of hell for denying it. See Nawawi.
Abdullah will fail the test on the day of judgement and hence be among the dwellers of hell. See Ibn Kathir.
The view that the ahl al-fitrah will be tested on the day of judgement is not correct. Actually there are different madhabs on their fate. Among them is that they shall be forgiven, and among them is that they will not be forgiven and will be in hell. The hadith could be taken as evidence for the last madhab.
Like any library, Islam Stack Exchange offers great information, but does not offer personalized advice or legal verdicts, and does not take the place of seeking such advice from your Mufti, Imam, or other trustworthy Counselor.