Is what was understood from fatwas no. 105903 and 107903, that the time for Maghrib extends until the disappearance of the twilight and that this is what is acted upon in Egypt, correct? And is it permissible to act according to that timing which makes the 'Isha' prayer time in winter an hour and a third after sunset, and in summer about an hour and a half?

The time for Maghrib extends until the entry of the 'Isha prayer time, with the disappearance of the red twilight. It is not determined by a specific time but by a sign. For those who do not know this sign, they may rely on trustworthy calendars. There is no harm in delaying the Maghrib prayer until the end of its time to remain in a state of ablution for 'Isha, but caution should be exercised not to delay it excessively. It is preferable to perform it after an hour or 45 minutes. However, it is most virtuous to perform it at the beginning of its time.