Well, the Vespers ought to be an actual rite. If they are OCD that would be the Carmelite edition of the Brev. Rom. If they are O.Carm. it would be according to the Carmelite Rite, unless you wish to do LOTH, which I believe both have adopted. But you have indicated four psalms, so I have guessed that you do not wish to use LOTH. The Hassler is a bit tricky if the books use the Urban hymns; I don’t remember if the AMS was edited in the 1620s, but honestly, immemorial custom.

The verse and response after the hymn has a simple tone (also used in the new rite for “Laus tibi, Christe”). The “Domine adjuvandam/Gloria Patri” is easy enough since all three parts (including “Deus in adjutorium”) are sung to the same melody. Ditto for the “Deo gratias” and “Amen” after “Benedicamus Domino” and “Fidelium animae” (hopefully they parrot the lowering of the voice for the latter). You can use a simpler BD if necessary. There aren’t really responses otherwise... There is a “Deo gratias” at the chapter and the response to “Dominus vobiscum” and an “Amen” at the collect. But the congregation is still engaged, such as during the incensation at the Magnificat. Depending on the mode of the antiphon on the Magnificat, there are several easy alternatim settings. The antiphons, being doubled according to the feast day (i.e. sung in full before and after) can be sung by the people if they have heard it before. Or, you can sing it to some kind of chant and then choose whatever Magnificat you want to allow for the alternation, such as the Grassi in 8G or the Parisian tone.

As far as not solemn goes, Fortescue is pretty clear on how to do it in a parish church without coped cantors and whatnot.

There are a number of Carmelite chant books in an obscure place over at musicasacra.com here.

I would go with the last of these, which is from 1959, and is titled Proprium Missarum et Officium Ordinis Carmelitarum Discalceatorum ; see p. (43) for 1st Vespers, sung on the eve of the feast.

There are 5 psalms (which is the case with the Roman form of the Divine Office), the same ones as are used in the common of feasts of Our Lady, to wit:

Ps. 109 - Dixit Dominus
Ps. 112 - Laudate pueri
Ps. 121 - Laetatus sum
Ps. 126 - Nisi Dominus
Ps. 147 - Lauda Jerusalem

Which all may be quite beside the point, as I would really think that the first step in planning this sort of thing is to find out from whoever is in charge what the "book" is.

Because if you aren't going "by the book", it's not vespers.

No?

Thanks for the link. But, we need to know if the friars are OCD or O.Carm first!

I understand that. But, one could very easily find a book that has semidoubled antiphons for the Little Hours of that day. I do not known when the last edition of the Carmelite rite breviary was published. And actually, the OCD book should have the old system...

I also will put my cards on the table here: devotional Vespers which mix and match rites or use the vernacular for the ancient offfices really annoy me... It means that you’ve put on a nice concert organized like worship, and if a cleric attends, he’ll discover he has to go home and pray Vespers.

Right, but see their breviary above, last revised in 1959. Even if 1960 rubrics apply, and honestly, I don’t usually observe them myself, the book itself would not have them.

They would be OCD. They have a house for students at my alma mater.

Hey, that’s quite a generous response. Good for him.