A. There is a Yiddish saying, “Every child brings its own blessing into the world”. This could be extended to every marriage. My experience of conducting weddings is that no two marriage ceremonies are the same, and there ought to be something personal about each one.
A few times in my career I was asked to conduct a double wedding and in applying halachic principles I said that I wanted each wedding to have its own personality. The halachah has a general doctrine, Ein m’ar’vin simchah b’simchah – “We do not mingle one celebration with another” (Mo’ed Katan 8b). The sages give the example of having a wedding on Chol HaMo’ed (the intermediate days of Pesach and Sukkot) and they talk about each celebration being given its own attention.
As far as weddings are concerned, the usage I followed was to have the first wedding late in the day and then a time gap to enable the second wedding to proceed at the beginning of the next Hebrew day. There was one combined wedding reception afterwards. In some places (I believe Britain is an example) it is permitted by the rabbinic authorities to have the two weddings follow each other on the same day.
The Shulchan Aruch points out that if there is a joint wedding feast for both couples, the sheva b’rachot (Seven Marriage Blessings) can be said jointly after the grace After Meals (Even HaEzer 62:3).