Was the guidance of the Prophet (peace and blessings be upon him) regarding marriage represented by men gathering for the عقد (marriage contract) between Maghrib and Isha in the mosque, and women and the bride gathering in the house of the husband or her family, and then the husband praying Isha and entering upon his family?

The command to conduct marriage in mosques is mentioned in a weak hadith. As for performing it between Maghrib and Isha prayers, there is no evidence for it. In the past, the contract was oral, but due to changes in people's circumstances, written documentation has become necessary. The testimony of women in a marriage contract is not considered valid, but there is no harm in their presence, provided they adhere to the manners prescribed by Islamic law and are separated from men, or gather in a place other than the mosque. There is no harm in a man entering upon his wife after the Isha prayer, but there is no text indicating its sunnah status.