There is no correct posture other than standing. The GIRM does not dictate anything else, although many individuals feel they are liturgically correct in their commentary based on what they like or don’t like.
This discussion has been going on since about 1965 or '66, and Rome has known of it for the greater majority of the time, and has specifically chosen to make no rules, in spite of specific opportunities to do so.
People get really heated about the matter. `
We have several here who have said that holding hands is not permissible, but have no citation. There is none.
And while I appreciate that Fr. McNamara teaches liturgy in Rome and answers questions for Zenit (the news agency). I also appreciate that the one in charge of the liturgy in a diocese is the bishop, and that individual is actually “in the trenches” in the US, and (from the response) inundated with this question.
I refer to archbishop Chaput - not exactly one of your “progressive” bishops, who some years ago, out of frustration (at least from the length and comments in the letter) wrote a public letter on holding hands.
His summary is that there is no rule, that Rome has been overlooking the matter in several renditions of the GIRM, and if one wants to hold hands, there is nothing liturgically wrong nor any rule violated; and if one does not want to do so, they should be allowed to not join in, and that both sides need to learn and engage in charity to those of a different mindset.
In short - there ain’t no rule. And all the hedging about it comes from those who either are not aware of how widespread and long it has occurred, or don’t like it.
It has been going on for 50+ years - I have a picture of college students in about 1966 holding hands during the Our Father. Likely source of the practice is from the Charismatic Movement.
Once upon a time, in the forum, a comment was made that any practice which has occurred consistently and widely for 40 years is, until specifically reversed, a de facto accepted practice. Whether or not that is true I leave to others trained either in Canon law or other law sets of the Church. It appears to be more widespread than the orans position, and it was the orans position that the USCCB at one point was going to petition Rome (and then withdrew from doing so, leaving the practice effectively in place).
Anything to the contrary is a personal opinion, with the exception of the USCCB (and those guys are actual liturgists…) which says… there is no rule.