Regarding the Prayer of the Faithful, from the 2002 General Instruction of the Roman Missal (GIRM) approved for the USA, which can be accessed from
romanrite.com/girm.html :
“138. After the recitation of the Creed, the priest, standing at the chair with hands joined, by means of a brief introduction invites the faithful to participate in the Prayer of the Faithful. Then the cantor, the lector, or another person announces the intentions from the ambo or from some other suitable place
while facing the people, who take their part by responding in supplication. After the intentions, the priest, with hands extended, concludes the petitions with a prayer.”
It is saying a person, one person. The person is to face the people. So people in the congregation calling out prayers is not following the 2002 GIRM.
The 2002 GIRM includes: “32. Special celebrations of Mass should observe the guidelines established for them: For Masses with special groups, cf. Sacred Congregation for Divine Worship, Instruction Actio pastoralis, on Masses with special groups, 15 May 1969: …”. If you are part of a “special group” the 1969 Instruction includes:
“6. … h. The general intercessions, always with respect for their religious character, may be adapted to the special circumstances. Care is to be taken, however, against complete omission of the general intentions for the Church, the world, brothers and sisters beset by needs, and the assembly present. Those present at the rite may add some particular intention, properly prepared ahead of time.”
(Documents on the Liturgy 1963-1979, Liturgical Press, Minnesota, 1982, ISBN 0-8146-1281-4, page 674).
It seems to me, if it is to be “properly prepared ahead of time” it should be written down so it can be proclaimed from the proper place, as described in the 2002 GIRM. But other interpretations of this are possible.
Regarding people being the sanctuary, around the altar, from the 2002 GIRM:
“294. The People of God, gathered for Mass, has a coherent and hierarchical structure, which finds its expression in the variety of ministries and the variety of actions according to the different parts of the celebration. The general ordering of the sacred building must be such that in some way it conveys the image of the gathered assembly and allows the appropriate ordering of all the participants, as well as facilitating each in the proper carrying out of his function.
The faithful and the choir should have a place that facilitates their active participation.
The priest celebrant, the deacon, and the other ministers have places in the sanctuary. Seats for concelebrants should also be prepared there. If, however, their number is great, seats should be arranged in another part of the church, but near the altar. All these elements, even though they must express the hierarchical structure and the diversity of ministries, should nevertheless bring about a close and coherent unity that is clearly expressive of the unity of the entire holy people. Indeed, the character and beauty of the place and all its furnishings should foster devotion and show forth the holiness of the mysteries celebrated there.”
Why should a priest follow the GIRM? The Code of Canon Law includes canon 846 “The liturgical books, approved by the competent authority, are to be faithfully followed in the celebration of the sacraments. …” (The Code of Canon Law: New revised English Translation, HarperCollins Liturgical, 1997, ISBN 000599375X.)
Before a priest is ordained he takes an Oath of Fidelity, which includes “I shall follow and foster the common discipline of the whole Church and I shall observe all ecclesitical laws, especially those which a contained in the Code of Canon Law.” Before someone is ordained as a bishop the words of the oath are “… I shall insist on the observance of all ecclesiatical laws, especially those which are contained in the Code of Canon Law.” (John Huels, The Pastoral Companion, Franciscan Press, 1995, ISBN 0-8199-0968-8, page 379.)