all of us here gathered for Mass

[Gemelle]

I will bless the image with Holy Water and also all of us here gathered for Mass.
Benedico l'immagine con l'acqua santa e anche noi tutti qui raccolti per Messa/per la Messa.


I always have doubts about whether to use or omit the definite article.
I'm not sure if "raccolti" is right here either.

 

[bise]

I think your translation is fine...
I just would put "con l'acqua santa" before "l'immagine" (in this way it sounds as the image contains holy water and I guess, instead, that the priest bless with holy water the image...)

"Benedico con l'acqua santa l'immagine..."

"Raccolti" is perfect!

"per la messa". In this case you should use the article...

 

[Blackman]

Riuniti is better than raccolti, IMHO.

 

[entrapta]

For me too; "riuniti per la Messa".

 

[bise]

Yes, definitely!
Even if "raccolti" is right, "riuniti" is just perfect... even the priest says "qui riuniti" during the Mass