What is the correct time to follow for the Fajr and Maghrib adhans in Ramadan when there is a discrepancy in timings between two mosques in the Netherlands, and a further discrepancy with internet timings, taking into consideration that one mosque is run by Turks and the other by Moroccans?

Prayer times are defined by religious texts and depend on natural signs:

Fajr (Dawn): The appearance of the true dawn and the horizontal spread of its light. Dhuhr (Noon): The sun declining from the middle of the sky. Asr (Afternoon): The shadow of everything becoming equal to its length, after the shadow at zawal (midday). Maghrib (Sunset): The complete disappearance of the sun's disc, with no consideration given to the remaining red afterglow. Isha (Night): The disappearance of the red afterglow from the horizon.

If it is difficult for a person to distinguish these signs, there is no harm in following a mosque whose caretakers are trusted.