All the caveats about whether the 'missing couple' actually exist apply, but I'm just running with the possibility.
It is only a newspaper report from the Express and so there may be reliability issues, but a few quotes stood out:
(a) It is believed they entered the bedroom on May 2, 2007, the evening before Madeleine disappeared from the Ocean Club at Praia da Luz on Portugal’s Algarve.
(b) It is already known that Pamela Fenn, who lived directly above apartment 5a, heard a child, believed to be Madeleine, crying for about an hour on the evening of May 2.
Mrs Fenn stated:
She also refers to the day of the 1st May 2007, when she was at home alone, at approximately 22.30 she heard a child cry, and that due the tone of the crying seemed to be a young child and not a baby of two years of age or younger.
At about 23.45, an hour and fifteen minutes after the crying began, she heard the parents arrive, she did not see them, but she heard the patio doors open, she was quite worried as the crying had gone on for more than an hour and had gradually got worse.
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There is a mismatch in dates, but this is quite possibly an error in the report/statements, so it is possible this all happened on the same night.
Mrs Fenn states 'she heard the parents arrive, she did not see them.'
It would not appear to be certain that the parents entered the apartment, as reported by Mrs Fenn, because she did not see them, it could have been the 'mystery couple'.
If the mystery couple do exist then I'm speculating that the people reporting seeing the mystery couple and the mystery couple are one and the same, and that the purpose of the entering the apartment was, as reported “Apparently they were concerned about the crying and went to see if they could comfort the girl.”