I’ve actually seen these take place myself as well… In these interactions, there are at times, jokes being made, with laughter, talking back and forth from pastor and someone in congregation, etc.
Usually, servers, the deacon, and the celebrant all entered the sanctuary not together, usually the celebrant beginning in the back of the sanctuary speaking/joking/making announcements from the back and as he makes his way up the center aisle. If he’s not done with what he is saying, usually the servers and deacon get to their respective seats near the altar and sit or stand there, until he is done speaking.
Once finished, he usually goes up to the chair next to the altar, says, “let’s pause for a moment before we celebrate the Eucharist together,” sits down for 10 or so seconds, before standing and opening the hymnal as the cantor(s) sing the chosen processional hymn for the day. However as omitted above, there is no processional.
I think both the friend who emailed me and myself were wondering if
A) such an entrance was licit,
B) if a processional hymn is allowed to be sung when there is no procession into the sanctuary since the ministers and assistants are all at the altar already.
I hope all of this helps clarify things.